Abstract: Abstract: To increase the yield in agriculture, plants must be protected against diseases and need to be provided with fertilizers. One of the most important methods to spread agro-chemicals is by using spray booms. The efficiency of the chemicals is highly correlated with the uniformity of the spray distribution pattern, and as spray boom motions play a dominant role on the spray distribution pattern, spray boom stability is important. Moreover, with the stable boom, the distance between the nozzles and the target can be reduced, and then the drift losses are less important. Boom movements are due to ground irregularities that are transformed and more or less amplified depending on the mechanics features of the boom suspension. In order to reduce the unevenness in spray deposit, the majority of current agricultural sprayers are equipped with a suspension system to attenuate the roll of the boom. The suspension tries to keep the boom at right angles by isolating the boom from vibrations of the tractor or trailer which are induced by unevenness of the ground. Therefore, the suspension system should act as a system that attenuates undesired machine movement. The most important vibration, affecting the spray distribution pattern, is rolling (rotational motion around an axis along the driving direction) that causes spray boom motions in the vertical plane. However, the correlation between the dynamic behavior of the spray boom and suspension parameters are still unclear and the design principles and methods of the pendulum boom suspension are also missing or imperfect, which restrict the improvement of spray quality and operation efficiency. In order to understand the effect of the dynamic parameters of pendulum suspension system on the dynamic behavior of the spray boom, an analytical mathematical model of this pendulum suspension is established by using the second kind of Lagrange equations and the necessary transfer function. The dynamic characteristics of the pendulum suspension are derived, and the behavior such as the rolling movement and vertical movement of the passive suspension can be most conveniently described by its complex frequency response function. Transient response analysis and frequency response analysis are carried out in MATLAB/Simulink, and the effects of dynamic parameters on the characteristics of the suspension are studied. On the basis of this, taking a large spray boom and its pendulum suspension as the test object, the boom rolling movement and vertical movement excitations were outputted by using the six degrees of freedom motion simulation platform, and the boom suspension was instrumented with ultrasonic distance sensor, LVDT (linear variable differential transformer) displacement sensor, and so on. The transient dynamic response and frequency response characteristics of spray boom were measured, and then the accuracy of the mathematical model was verified. The root mean square error between the mathematical model predictive value and test value was 0.146 for rolling frequency response, and 0.203 for vertical oscillation frequency response. Peak value of the amplitude frequency curve and the corresponding frequency were determined by the sweep frequency vibration test, and the influence of damping and stiffness coefficients on the vibration characteristics of the boom was analyzed. In a certain range, increasing the damping could reduce the system oscillation and increase the stiffness, which was beneficial to increase the response speed and natural frequency of the suspension, but natural frequency could not be too high since beyond this frequency the suspension started to suppress the disturbances. Through research, we get to know that this kind of pendulum suspension with springs and dampers can enable the boom to follow low frequency ground undulations so remaining parallel to the ground beneath it, while providing isolation from the rapid motion of the spray vehicle as it travels over rough terrain. This study also provides a theoretical basis and test method for the parameters configuration of large boom, and it is beneficial to perfect the test method and test standard of the dynamic characteristics of large scale spraying boom (over 12 m) in China.