Abstract: In this paper, in order to obtain a method of increasing the power output of the downstream wind turbine by reducing the wake effect of the upstream wind turbine, NREL 5 MW wind turbines were used as research objects, and we coupled large-eddy simulation with an actuator line technique based on OpenFOAM open-source software as our numerical method. Firstly, the Gaussian width (ε) in the actuator line model was studied at the rated wind speed, we found that the error of the calculation result was the smallest when there were 50 mesh nodes along the direction of rotor diameter and ε was 1.6 times grid scale; Secondly, numerical simulations were carried out for a single wind turbine with tip-speed ratios (λ) of 15, 10, 8 and 7, respectively (corresponding to inflow wind speeds was 3, 5, 7, 11.4 m/s). It was found that the wake velocity distribution was “W” type in the near-wake of the wind turbine, and with the development of the wake, the wake velocity distribution was “inverted bell” type in the far-wake of the wind turbine. The wake velocity distribution of wind turbine was related to λ. When λ was larger, the velocity loss in the near-wake field was larger, and the velocity of the wake field recovers faster. λ was smaller, the velocity loss in the near wake region was small, and the velocity recovery in the wake field was relatively slow. When λ was 15, 10, 8, and 7, respectively, the average speed loss at a position of 1 times rotor diameter (D) after the wind turbine was 45.7%, 42.4%, 38.8%, and 33.8%, respectively. When the wake developed to 18D, compared to the 1D position, the velocity recovered by 35.4%, 32.4%, 29.6% and 18.6% in order. Finally, through the numerical simulation of two wind turbines in tandem, two strategies by reducing the wake effect of upstream wind turbine to increase the output power of downstream wind turbine were studied. During the simulation, the distance between the two wind turbines was six times of the rotor diameter, and the inflow speeds was 5 m/s, 7 m/s and 11.4 m/s, respectively. It was found that when the hub heights of the two wind turbines were different or the upstream wind turbine had a yaw angle, the power output of the downstream wind turbine can be increased. Under the condition that the inflow velocity was 7 m/s , when the difference between the hub heights of the upstream and downstream wind turbines was 0.25D, 0.5D and 0.75D, respectively, compared with the situation of 0D，the power output of the downstream wind turbine increased by 1.36, 2.50, 4.50 times and the total power of the two wind turbines increased by 20%, 56% and 66%, respectively. When the yaw angles of the upstream wind turbines were 15°, 30° and 45°, respectively, compared with the situation of 0°, the power outputs of the downstream wind turbines increased by 1.58, 3.36, 4.26 times and the total rate of the two wind turbines increased by 18%, 30% and 22%, respectively. The above research results can provide reference for wind turbine selection in wind farms and increase wind farm power output by controlling operating conditions of upstream wind turbine.