Abstract: Knowing the influences of insect infestation on CO₂ volume fraction in grain storage environment and detecting the CO₂ volume fraction for monitoring pest occurrence are of great significance to pest and grain situation. The changes in ambient CO₂ volume fraction as well as its effects on kernel broken rate, thousand kernel weight and volume weight in 60 d were investigated after wheat samples with 12% moisture content were infested with four densities (0, 5, 10 and 30 adult/kg) of Cryptolestes ferrugineus (Stephens) adults at 30 ℃. In the initial 20 days of infection, the average increase rate per day (AIRPD) of CO₂ volume fraction in wheat environment with 0, 5, 10 and 30 adult/kg of Cryptolestes ferrugineus were 0.012%, 0.037%, 0.038% and 0.068%, and corresponding CO₂ volume fraction rose to 0.283%, 0.780%, 0.800% and 1.407%. During the 21th to the 35th day, the AIRPD of CO₂ volume fraction in environment with corresponding insect densities were 0.013%, 0.105%, 0.163% and 0.267%, and the CO₂ volume fraction rose to 0.473%, 2.357%, 3.240% and 5.407% in the 35th day. During the 36th to the 60th day, the AIRPD of CO₂ volume fraction in environment with corresponding insect densities reached 0.021%, 0.204%, 0.219% and 0.268%, and the CO₂ volume fraction rose to 0.993%, 7.447%, 8.713% and 12.107% in the 60th day. After infection for 60 days, the kernel broken rate increased significantly, but thousand kernel weight and volume weight had no significant changes. CO₂ volume fraction increased significantly after 9-day infection with 5 adult/kg or higher densities of Cryptolestes ferrugineus. Therefore, CO₂ volume fraction could reflect the occurrence of Cryptolestes ferrugineus to a certain extent, thereby realizing insect and grain monitoring.