Overview: The traditional method of the thin film transistor (TFT) lithography plane compensation is realized by ensuring the flatness of photoresist plane and the photoresist plane is on the focal plane of the lithography machine, which is achieved by the compensation of flatness of the plate stage and the focus compensation of lithography machine. However, due to the existence of the compensation error, the quality of the actual lithography product picture is different from the ideal situation, when the TFT line width or line space is close to the minimum resolution of the lithography machine. The difference will lead to the defect of remaining photoresist, which seriously affects the yield of the lithography products. In order to solve the problem, based on the position of the best lithography pattern, the optimal compensation amount of lithography plane of the lithography machine is calculated. The difference of the result between the actual lithography product and the compensation of the lithography plane is reduced by the optimal compensation, which is compensated for the lithography machine. 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 lithography region. Then, according to the lithography pattern in the lithography region, the optimum position of the lithography region is found. Taking 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 lithography region tends to the same optimal lithography plane. The results show that, compared with no compensation, the lithography pattern can be clearly formed in the lithography region after the lithography plane is offset. The defect of the remaining photoresist is improved. At the same time, the average value of the DICD is reduced by 1.38% in the target value range, the uniformity of the DICD is increased by 20%, and the ability of small line lithography for the lithography machine at the minimum resolution has been significantly improved.