Uniform illumination free-form surface lens has been widely used in the light emitting diode (LED) lighting. However, due to modeling error in traditional freeform surface solution based on geometrical approximation, the surface shape can not be solved accurately and result in the decline of illumination uniformity. A method of error analysis and compensation algorithm is proposed. The relationship between emitted light angle error and free-form surface error is established, combined with the ray tracing, quantifying and correcting for surface error accurately. According to the method above, it is suggested that the compensation design of landscape lighting lens in which the working distance of the lens is 1000 mm and target panel diameter is 200 mm. The simulation result shows that after importing the lens modeling into Lighttools software demonstrate, compared with the traditional design method, the illumination uniformity is increased from 68.0% to 98.5% under the condition of point light source. And the uniformity is reached up to 91.8% with the diameter of 160 mm lighting area and the condition of 1mm×1mm size of the LED source. The optimized lens has good practicability.