The invention provides a parameter optimization-based low-illuminance image enhancement method. The image enhancement method includes the following steps that: a) a low-illuminance image R(x) is obtained, the enhancement function E (x)-(225-(A)=(R(x)-(225-A))/t(x) of the low-illuminance image R (x) and an enhancement image E(x) is built; b) the gray image g(x) of the low-illuminance image R(x) is normalized, so that the normalized gray image gray of the low-illuminance image R(x) is obtained; c) the linear correlation function t(x)=f(W,g(x)) of magnification times t for converting the low-illuminance image R(x) to the enhancement image E(x) and the normalized gray image gray of the low-illuminance image R(x) is constructed; and d) a sky brightness parameter A=255 and the linear correlation function t(x)=f(W, gray) are selected, so that an optimization enhancement function E(x)=R(x)/t(x)=R(x)/f(W, gray) is obtained so as to perform enhancement on the low-illuminance image.