Abstract: In an automatic gamma adjustment system with environmental adaptability, the system is installed in a display device and an image signal source is selected, such that an image signal is received and converted into first YUV signals, while detecting the surrounding situation to obtain at least one environmental data, and obtaining a gamma control parameter of a display screen of the display device according to the environmental data. When the environmental data is calculated to obtain a maximum brightness current value, the gamma control parameter is used to calculate the first YUV signals as second YUV signals, and the maximum brightness current value and the second YUV signals are sent to the display device for displaying the image. Therefore the grayscale layering effect of an image presented to people can be adjusted by automatically correcting the gamma value according to the surrounding situation at any time.