Disclosed is an adjusting method of a gamma voltage adjusting device. The gamma voltage adjusting device is utilized for providing a liquid crystal panel with N gray levels and includes a printed circuit board assembly and a gamma voltage fine-tuning unit. The adjusting method of the gamma voltage adjusting device includes: generating N+2 gamma voltages with the printed circuit board assembly; inputting the N+2 gamma voltages to the gamma voltage fine-tuning unit; and generating negative polarity driving voltages and positive polarity driving voltages which are symmetrical according to the N+2 gamma voltages. The present invention decreases a number of gamma integrated circuits on the printed circuit board assembly for saving cost by decreasing the 2N gamma voltages in the prior arts to the N+2 gamma voltages.