1. A method for calibrating brightness unevenness of an OLED display panel, wherein the method comprises the steps of: getting a brightness matrix of an OLED display panel in at least three gray scales, wherein the at least three gray scales comprises: a highest gray scale 255 and a minimum reference gray scale and a maximum reference gray scale set up by a reference gray scale when adjusting a Gamma; determining a uniform brightness area and an uneven brightness area based on the brightness matrix; measuring a found Gamma curve of the uniform brightness area, and calculating a fitting Gamma value of each pixel corresponding to the at least three gray scales in the uneven brightness area based on the brightness matrix; fitting the fitting Gamma value based on the found Gamma curve respectively to obtain a fitting Gamma curve of the each pixel in the uneven brightness area; calibrating the uneven brightness area by the fitting Gamma curve of the each pixel; the uneven brightness area calibrated by the fitting Gamma curve of the each pixel comprises: a gray scale—brightness correspondence table for calculating the each pixel by the fitting Gamma curve of the each pixel; finding the gray scale—brightness correspondence table of the each pixel to obtain a correction gray scale value of the each pixel, and calibrating the uneven brightness area by the correction gray scale value.