This paper investigates the diagonal inflow effect on the wake characteristics of a HAWT (Horizontal Axis Wind Turbine) in a wind farm. In this study, a HAWT with the generator capacity of 30 kW and the rotor diameter of 10.0 m is used. Firstly, the effect of pitch angle on the power and thrust performances of wind turbine are investigated through field experiment. On this basis, the wake characteristics of the HAWT are examined with different wind directions and pitch angles. The velocity field is measured by the ultrasonic anemometers, the three-cup type anemometer and the wind vane. Finally, the annual power generation of the downstream wind turbine is predicted by different Gaussian models. As a result, the maximum power coefficients Cp are 0.31, 0.33 and 0.27, corresponding to the tip speed ratios λ = 7.5, 7.4 and 6.8 and the pitch angles β = 0°, 2° and 4°, respectively. The standard deviations of wind direction are divided into four regions between σθ = 5° and 20°. The maximum deficit values of the wake velocity decreases from 0.27 to 0.16, and the full wake widths at half maximum Dr increases from 1.35 to 1.71 with σθ increasing from 5°∼9°–14°∼20°. The amount of annual energy production predicted by the wind tunnel experiment model is about 51 % of the field experiment model. This study provides a better understanding of the wake characteristics and a guiding significance for the layout optimization of wind farms.