With the rapid construction of large-scale wind farms, the upstream wind turbine will deteriorate the wind velocity in the wind turbine wake region and increase the wake turbulence, thereby reducing the power efficiency of the downstream wind turbine and aggravating the fatigue damage of the wind turbine to shorten its service life. Therefore, it is urgent to carry out the study of wind turbine wake characteristics. The main purpose of this study is to reveal the wake characteristics of a standalone wind turbine under different upstream flow conditions and with various yaw angles. Firstly, the accuracy of Large Eddy Simulation (LES) combined with Actuator Line Model (ALM) was verified by the corresponding wind tunnel test. And then, based on the LES-ALM simulation method, the effects of inlet (including velocity and turbulence intensity) and yaw angle on the turbine wake characteristics were studied, and the symmetry of the horizontal profiles of the wind turbine wake at the hub height was clarified with positive and negative yaw angles. The results show that with the increase of the background turbulence intensity, the recovery of the wind turbine wake will be accelerated. Moreover, under the same upstream flow conditions and symmetrical yaw angle, the certain symmetry of wind turbine wake velocity was also identified. When the yaw angle of the wind turbine increases, both the expansion rate of the turbine wake width and the deficit degree of the wake wind velocity would decrease.