Abstract: Abstract: Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Heat transfer fluid is heated by sun rays through the solar concentrator, then used as a heat source for a conventional power plant. A wide range of concentrating technologies has existed; the most developed are parabolic trough collector (PTC), linear fresnel reflector system (LF), power tower, and dish/engine system (DE). Parabolic trough collector is considered as one of the most mature applications of solar energy in these four technologies, which makes it worth developing. Sun-tracking system plays an important role in the development of solar energy applications, especially for the high solar concentration systems that directly convert the solar energy into thermal or electrical energy. High accuracy of sun-tracking is required to ensure that the solar collector is capable of harnessing the maximum solar energy throughout the day. Compared to fixed systems, power output of single-axis and dual-axis tracking systems can increase by 25% and 41% respectively under the same condition. It is clear that an accurate sun-tracking control system can make solar collectors receive more solar radiation energy to improve the solar energy utilization. A good sun-tracking system must be reliable and able to track the sun at the right angle even in the periods of cloud cover. Although the tracking system is more complex and costs higher than the fixed system, increasing the annual output power can reduce cost effectively. As for photoelectric tracking mode, a sun position sensor is used to provide feedback signals to judge where the sun is, but they don't work on cloudy days because of the lower sensitivity. The stability of the solar tracking system is a key factor to obtain the maximum sunlight from parabolic trough collector. In order to improve tracking stability and accuracy of the parabolic trough collector sun-tracking control system, this paper chose the more reliable hydraulic drive mechanism to match the system and mainly focused on the design of sun-tracking control system and analysis of operational data from the parabolic trough collector sun-tracking system. Based on the existed working platform of parabolic trough collector system with a length of 50 meters, this paper developed a sun-tracking control system for parabolic trough solar collector. Based on programmable logic controller (PLC), active control mode on the trajectory of the sun was adopted, which could calculate the rotation angle of the parabolic trough solar collector and control commands to drive the hydraulic cylinder to achieve real-time tracking of the sun. The system's basic operating principle, design of sun-tracking, rotation angle algorithm of parabolic trough solar collector and PLC's programs have been analyzed. Experiments were conducted in the 4 typical dates (March 20, June 21, September 23, and December 22, in 2013). The analytical result showed that sun-tracking errors of parabolic trough solar collector were nearly 0.5°. Compared to more accurate SPA (solar position algorithm) algorithm, calculation error of algorithm to calculate the position of the sun was within 0.12°. The maximum error of intermittent operation tracking mode was within 0.398°. The maximum operating speed of parabolic trough collector in the year appeared at noon on the winter solstice, the maximum operating speed was 0.398°/min, and transmission error of an angle sensor was at 0.044° or less. This study may provide the theoretical basis for mechanical transmission design of parabolic trough collector.