1. A shooting parameter adjustment method for face detection, comprising: (A) acquiring an image; (B) dividing the image into a plurality of first blocks, (C) averaging each of at least one part of the first blocks to acquire a brightness value of each of the first blocks; (D) ordering the brightness values of the first blocks according to brightness value; (E) averaging N th to (N+M) th brightness values of the first blocks to acquire an average value of the N th to (N+M) th brightness values of the first blocks; (F) adjusting a shooting parameter according to the average value of the N th to (N+M) th brightness values of the first blocks; (G) acquiring another image according to the adjusted shooting parameter, and performing a face detection procedure on the image acquired in (G)to determine whether any face exists in the image acquired in (G); and (H) repeating the steps (B) to (G), if no face exists in the image acquired in (G); wherein when no face exists in the image acquired in (G), averaging (N+1) th to (N+M+1) th brightness values of a plurality of second blocks of the image acquired in (G) to acquire an average value of the (N+1) th to (N+M+1) th brightness values of the second blocks, and then adjusting the shooting parameter according to the average value of the (N+1) th to (N+M+1) th brightness values of the second blocks.