We conducted research to confirm the applicability of a soil CO2 measurement system to estimate changes in the level of soil carbon storage. We monitored the soil surface CO2 efflux (Fc), layer CO2 concentration (Cc), temperature (Ts), and moisture (ϴ) monthly from September 2018 to September 2020 at 18 locations in a 20-year-old Pinus koraiensis stand in South Korea. The recorded average Fc, Cc, Ts, and ϴ were 519.8 mg C m−2 h−1, 1775.7 ppm, 12.1 °C, and 13.9%, respectively. The observed Fc and Cc values increased during the growth season (April–October); however, Fc (Q10 = 2.19) was more sensitive to temperature changes than Cc (Q10 = 1.74). To investigate the effects of ϴ on Fc and Cc, they were normalized at Ts = 10 °C to F10 and C10. To perform regression analysis, Fnorm and Cnorm were calculated by normalizing Fc and Cc to minimize the temperature effects. This ϴ did not explain Fnorm and Cnorm well as a single independent variable. However, according to the results of multiple nonlinear regression analyses, C10 and ϴ explained approximately 70% of F10 (p < 0.0001). To estimate the precise levels of soil carbon storage, it is essential that various types of forest and climate conditions be monitored.