The invention provides a constant grinding force PID (Proportion Integration Differentiation) control optimization method based on an improved firefly algorithm. The method is characterized by comprising the following steps: step 1, initializing basic parameters of the algorithm; step 2, randomly initializing positions of fireflies, and calculating a target function value of each firefly as respective maximum fluorescence brightness I0; step 3, calculating the relative brightness I and attraction beta of the fireflies in a colony according to a relative fluorescence brightness formula and an attraction formula of the fireflies, and determining the moving directions of the fireflies according to the relative brightness I; step 4, updating spatial positions of the fireflies according to a position updating formula of the fireflies, and reserving the positions of lighter fireflies; step 5, recalculating the brightness of each firefly according to the updated positions of the fireflies; step 6, turning to next step if a maximum number maxT of iterations is achieved, otherwise, adding to the number of searches and turning to step 3 for next search; and step 7, outputting global extreme points and position values of optimal individuals.