Soil CO2 concentration is the consequences of biological activities in above- and below-ground, and its fluctuation may significantly affect the future atmospheric CO2 concentration and the projected climate change. This paper reviewed the methodologies for measuring the soil CO2 concentration in situ as well as their advantages and disadvantages, analyzed the variation patterns and controlling factors of soil CO2 concentration across the temporal (diurnal, several days, seasonal and inter-annual) and spatial (soil profile, site and landscape) scales, introduced the primary empirical and mechanical models for estimating and predicting soil CO2 concentration, and summarized the applications and constraints of soil CO2 concentration gradient in determining soil respiration. Four research priorities were proposed, i. e., to develop new techniques for collecting and determining the soil CO2 in severe soil conditions (e. g., flooding, lithoso and others), to approach the responses of soil CO2 concentration to weather change and related regulation mechanisms, to strengthen the researches on the spatial heterogeneity of soil CO2 concentration, and to expand the applications of soil CO2 concentration gradient in the measurement of tropical-subtropical soil respiration.