This article studied the rule of flow separation in low-rise building with flat roof through the combination of experimental method and numerical simulation, when the wind speed is 7 m/s and the turbulence is less than 10%. The results indicated that the mean wind pressure coefficient and extreme wind pressure coefficient of the roof decreased when applying along-wind plasma actuation; The mean wind pressure coefficient and extreme wind pressure coefficient increased in the front portion of the roof, and decreased in the back portion of the roof when applying headwind plasma actuation; The mean wind pressure coefficient and extreme wind pressure coefficient increased in the front portion of the roof and decreased in the back portion of the roof when applying the plasma actuation from middle to the both sides; The mean wind pressure coefficient decreased in the front portion of the roof and in the back portion, and the mean wind pressure coefficient and extreme wind pressure coefficient increased in the middle portion of the roof when applying the plasma actuation from the both sides to middle. The results of this paper can provide reference for wind resistance studies of building.