Analysis of three different methods of estimating CO₂ emission was carried out by comparing the data obtained from filed determination of soil CO₂ emission from Mat Cryo-sod soil in 1998~1999. Based on the results of the analysis a suitable method of estimating CO₂ emission form Mat Cryo-sod soil was developed. The equation for estimation of diel CO₂ emission is a monadic biquadratic multinomial with instantaneous CO₂ emission flux as dependent variable and time as drive variable. And by deriving the integral to time, the values of the diel CO₂ emission can be obtained. For estimation of annual emission, a multi-nonlinear experiential formula was established with diel CO₂ emission as dependent variable and environment factors as drive variable (such as precipitation, evaporat ion, sunshine, air temperature, soil temperature, etc.). Diel CO₂ emission was calculated using related data from the meteorological station every day, and then the annual accumulated CO₂ emission was obtained.