The objective of this study was to investigate the effect of low frequency alternating magnetic field (LF-AMF) on the production of extracellular polysaccharide (EPS) by submerged liquid fermentation of Pleurotus citrinopileatus. The fermentation conditions optimized by central composite design method were as follows: fermentation time of 6 d, temperature of 28 ℃, shaking speed of 150 r/min, and inoculum amount of 8 %. Under these conditions, a LF-AMF was applied to the liquid fermentation of P. citrinopileatus. When the intensity of LF-AMF was 40 Gs, the initial intervention time was 24 h after inoculation, and the treatment time was 6 h at one time, the mycelium biomass of P. citrinopileatus increased by 11.30 ± 0.33 %, and the EPS yield increased by 23.09 ± 1.52 % compared with the fermentation without LF-AMF treatment. The morphology of mycelium after LF-AMF treatment was observed by scanning electron microscopy. It was found that the surface of mycelium was wrinkled and the structure of mycelium was loose, which might be more conducive to the production of EPS.