In the process of biomass storage and transportation, there exists the phenomenon of self-heating caused by microbial growthand metabolism heat production, which may cause spontaneous combustion of biomass. Water content is an important factor affecting microbial growth, metabolism and heat production. In this paper, a 120 L self-heating insulation test chamber was designed and built. Theeffects of water content on self-heating characteristics of corn straw were studied in the range of 20%-95% water content. Temperatureand oxygen consumption rate were used to characterize the degree of self-heating and microbial metabolic activity, respectively. The results show that the maximum temperature and peak heat production of corn straw in the process of self-heating increases firstly, and thendecreases with the increase of moisture content. The maximum temperature is 41.1 ℃ under 50% moisture content, and the maximumpeak heat production is 157 J/ (s·m3) under 80% moisture content. The peak heat production of corn straw is affected by moisture content. When the water content is lower than 35%, the difference of peak heat production is small. When the water content is between 35%and 80%, the peak heat production shows a linear relationship with the water content, and the average increase of peak heat production is33.43 J/ (s·m3) when the water content increases by 15%. When the water content exceeds 80%, the peak heat production decreases.The specific growth rate of microorganisms is directly proportional to the oxygen consumption rate, and both of them increase firstly, andthen decrease with the increase of water content. The oxygen consumption rate reaches the maximum value of 0.056% / min under 80% water content, indicating the strongest metabolic activity of microorganisms. The research results provide reference for analyzing the selfheating characteristics of corn straw and proposing the safe storage and transportation measures of biomass.