Straw mulch is a very common measure during wintry fallow period that can last more than five months in southern China. However, few studies have investigated the effects of straw mulch during the winter fallow season. Experiment was started at Taoyuan Agro-ecological station of the Chinese Academy of Sciences to find out the effect of straw mulch on agro-ecosystem and settle a foundation of exploring economically feasible and eco-friendly mulching option. Two treatments were set: with 4000 kg·hm-2 straw mulch in winter and 3500 kg·hm-2 straw mulch in late spring per year and CK. Both treatments were replicated twice in a complete randomized block design. Through the experiment, we monitored the dynamics of soil temperature and moisture, CO2 fluxes from the wintry paddy ecosystem, and investigated the growth of weeds. The results showed that straw mulching on wintry fallow paddy would be heat preservation, the temperature of upper layer (0-5cm) was 1.0-3.2℃ higher than CK; Mulching significantly retarded the loss of soil moisture in surface layer (0-15cm), and also restrained the growth of weed. Furthermore, mulching strongly influenced the CO2 fluxes between agro-ecosystems and atmosphere. During the experiment, while CK fixed 4.13 tCO2·hm-2 from atmosphere, the mulched treatment released 3.06 tCO2·hm-2 into air.