A novel line focus system with active optics for X-ray laser research is suggested. It consists of a active mirror, a cylinder lens and a aspherical lens. The Intensity distribution of line focus is uniform and its length can be tunable continuously in certain range. In this paper, the profile along the line focus is simulated and analyzed in details based on the principle of physical optics. With respect to the incident laser beam with Gaussian intensity, the possibility of controlling the line focus profile by active optics system is discussed.