The present disclosure provides a method for determining a width-to-length ratio of a channel region of a thin film transistor (TFT). The method includes: S1, setting an initial width-to-length ratio of the channel region; S2, manufacturing a TFT by using a mask plate according to the initial width-to-length ratio; S3, testing the TFT manufactured according to the initial width-to-length ratio; S4, determining whether or not the test result satisfies a predetermined condition, performing S5 if the test result satisfies the predetermined condition, and performing S6 if the test result does not satisfy the predetermined condition; S5, determining the initial width-to-length ratio as the width-to-length ratio of the channel region of the TFT; S6, changing the value of the initial width-to-length ratio, adjusting a position of the mask plate according to the changed initial width-to-length ratio, and performing S2 to S4 again.