Abstract: A field experiment with maize variety Liangyu 99 was conducted to investigate the effects of maize-mushroom intercropping under high photosynthetic efficiency planting patternon,analyzed the photosynthetic parameters,fluorescence kinetic parameters,5 key enzyme activities of photosynthesis,content of soluble protein,soluble sugar and starch,and maize yield in 2017 and 2018.Results showed that intercropping significantly enhanced air humidity and CO₂ concentration,and improved the microclimate in maize field.Intercropping significantly increased maximal photochemical efficiency(Fv/Fm) and the net photosynthetic rate(P_N) during the first(July 21) and second(August 11) Pleurotus ostreatus peak,respectively.At the second Pleurotus ostreatus peak(August 11),intercropping increased malate dehydrogenase(MDH)(P<0.05),malic enzyme(NADP-ME),phosphoenolpyruvate carboxylase(PEPC),pyruvate phosphate double kinase(PPDK),ribulose-1,5-bisphosphate carboxylase(Rubisco) activity,soluble protein,soluble sugar and starch concentrations,established the basis for photosynthetic products during the grain filling stage.The net maize yield increased by 376 kg·hm^-2in 2017 and 325 kg·hm^-2in 2018 compared to monoculture maize,and the land equivalent ratio was 2.5 and 2.4,indicating yield gain under intercropping.