Abstract: Organic fertilizer derived from intercropped legume and grain crops supplies substantial soil nutrient under intensive cropping system. Microbial biomass carbon and microbial biomass nitrogen, respiration CO₂ and mineralized nitrogen in plant straw fertilized soil were determined under laboratory incubation conditions of constant temperature and moisture based on field aboveground yields of intercropped sweet maize straw and white clover straw. Results show that microbial biomass carbon and microbial biomass nitrogen in fertilized soil peak in the first several days, and then decline. Intercropping Incubating both sweet maize straw and white clover have the highest yield, maxima of 529.57 mg·kg^-1 and 75.50 mg·kg^-1 respectively. They also release the most respired CO₂ the most among all treated soils. The best mineral nitrogen release is in white clover intercroppingincubating, with a maximum of 29.81 mg·kg^-1 under a 26-day culture, and then keeping 1.60 times the control and reaching 2.48 times at 80-day culture. Sweet maize incubatingintercropping has the least mineral nitrogen release. It is 13%~53% of the control under a 26-day culture, with a maximum of 7.51 mg·kg^-1. Soil nitrogen mineralizatiomineralization is insignificant under sweet maize incubatingintercropping with urea in short-term. It is concluded that plant straw intercropping fertilizing enhances soil organic matter turnover. Intercropping Incubating of sweet maize and white clover may induce significant higher soil microbial biomass. White clover incubating intercropping activates soil microbe which is beneficial to soil nitrogen mineralization.