The embodiment of the invention discloses a method for regulating exposure, which is characterized by dividing the lightness interval of a system into at least three subintervals in advance, respectively setting a fitting function for each subinterval, and presetting an object lightness value, an upper limit value and a lower limit value thereof. The method comprises the following steps: obtaining parameter values at the current time, wherein the parameter values comprise a lightness statistic value of an input image at the current time; when the lightness statistic value is not within the interval composed of the upper limit value and the lower limit value of the object lightness value, judging the subinterval to which the lightness statistic value belongs; and regulating the exposure through the fitting function corresponding to the subinterval to which the lightness statistic value belongs. The embodiment of the invention further discloses an exposure regulating device. The embodiment of the invention also discloses an exposure regulating device. Different fitting functions are set for different lightness intervals, so new grains and exposure times of different intervals can be calculated according to the different fitting functions in the exposure regulating process, thereby reducing overshoot and enhancing the stability of exposure control of the system.