Abstract: Abstract: CO2 flux in farmland is a significant component of the global carbon cycle, which is affected by agricultural management practices. The plastic film mulching is one of the most important measures applied in rain-fed agriculture, however, its effect on CO2 flux and soil respiration in rain-fed farmland has not been well evaluated. In order to determinate the effect of plastic film mulching on carbon flux and soil respiration in farmland and to understand maize yield as affected by the plastic film mulching from the perspective of carbon flux, an experiment of mulching was conducted since 2011 in Shouyang Dryland Agriculture Comprehensive Experimental Station, Shanxi Province, China. We monitored diurnal changes and seasonal changes of soil respiration, net carbon flux, topsoil temperature and moisture in the spring maize field with plastic mulching and un-mulching treatments by LI-8150 automated soil respiration measurement system and eddy covariance system, respectively. The leaf area index and dry matter of maize were also measured at a sampling interval of 6 to 10 d during the entire growing season. The results indicated that the general trend of seasonal changes of soil respiration in both plastic film mulching and un-mulching spring maize fields were similar. But the plastic film mulching inhibited the soil respiration and decreased the carbon emission significantly as compared to the un-mulching treatment. Soil respiration rates in the plastic film mulching field during the growing season were 0.24 to 3.61 μmol/(m2·s), which were smaller than un-mulching treatment of 0.60 to 5.24 μmol/(m2·s). The total amount of carbon emission from the mulching treatment was 158.95 g/m2, which only accounted for 61.7% of that in un-mulching field. At the same time we found that plastic film mulching had a beneficial effect on soil water and temperature regimes of topsoil which promoted the growth and increased final yield of maize. Compared with un-mulching, plastic film mulching treatment increased topsoil moisture by an average 18.7% for all maize growth stages and topsoil temperature by an average 1.6℃ at the early maize growth stage. The leaf area index of plastic film mulching treatment was higher than un-mulching treatment by an average 0.81 m2/m2 at early and middle stages, but lower by 1.00 m2/m2 at the harvest. The final aboveground and below ground dry matter of maize in plastic film mulching treatment was respectively 269.7 and 38.6 g/m2, higher than un-mulching treatment. The grain yield was 1348 kg/hm2, higher than that of un-mulching treatment. Due to the effects of mulching on soil respiration, maize growth and leaf area index, the daily average net carbon flux of un-mulching treatment was higher than plastic film mulching treatment by an average 0.04 mg/(m2·s) at the early and middle maize growth stages, but only lower by an average of 0.02 mg/(m2·s) at the late growth stage. The final net carbon accumulation of plastic film mulching treatment was 596.0 g/m2, which was significantly higher than 505.8 g/m2 of un-mulching treatment. This study suggested that plastic film mulching increased topsoil temperature and moisture, promoted spring maize growth and carbon accumulation, inhibited soil respiration, increased farmers' income through high maize yield and also helped for soil carbon management.