When the line width or line space of thin film transistor (TFT) is close to the resolution of the lithography machine, it is easy to appear the defect of photoresist remain in lithography pattern. In order to improve this problem, based on the position of the best lithography pattern, the optimal compensation amount of lithography plane of the lithography machine is calculated, so lithography plane is improved. Firstly, by the compensation of the lithography plane, the flatness of the plate stage and the focal plane, the value of the plate surface height is calculated in the li-thography region. Then, according to the lithography pattern in the lithography region, the optimum position of the lithography region is found, and take this location as the zero point, the relative height difference between the total lithography region and the optimum position is calculated. Secondly, the fitting plane of the height difference in the lithography region is done, and the compensation is calculated when the fitting plane is the horizontal plane that is perpendicular to the Z axis, which is the optimal compensation of the lithography plane in the lithography region. Finally, the compensation is used to compensate the lithography plane, so that the lithography plane in the litho-graphy region tends to the same optimal lithography plane. The results show that the lithography pattern can be clearly formed in the lithography region after the lithography plane is offset, the defect of the photoresist remain is improved, at the same time, the average value of the develop inspection critical dimension (DICD) is reduced by 1.38% in the target value range, and the uniformity of the DICD is increased by 20%.