The development of biomass gasification is subject to low quality of gas with low heating value and high tar concentration. A new biological pretreatment method by using biogas slurry (BS) with different moisture content (40-80 wt%) and retention time (1-7 days) was advanced for promoting air gasification of corn straw (CS). The considerable NH4+-N, appropriate pH and abundant microbes in BS made it effective for CS pretreatment. The dry matter loss of pretreated CS was recorded, the properties of CS and the pretreated CS were comparatively analyzed, and also the kinetic studies. Air gasification experiments were performed in a horizontal tube furnace at 1000 degrees C. The delignification reaction of BS made disordered and incompact structure of CS with the improved surface area, and decreased the activation energy for chemical reaction. The higher moisture content and longer retention time contributed to the optimal gasification performance. Considering the time and energy conservation, the intermediate 60 wt% moisture content and retention time 5 days was proposed. Compared with the raw CS, the LHV (7.15 MJ/Nm(3)) increased 1.15 MJ/Nm(3), and tar content decreased 21 wt%. This proved efficient and low cost to produce bioenergy from CS, meanwhile, reducing BS and minimizing its potential pollution.