In this study, the effect of conservation tillage on soil organic matter (SOM) in paddy rice cultivation after 10 yr was investigated. Four treatments, disk till-fallow (DTF), disk till-wheat (DTW), conservation till-fallow (CTF) and conservation till-wheat (CTW) were used. The results indicated that the combinative application of no tillage, ridge culture and wheat cultivation was a sound conservation practice in paddy rice cultivation. It not only significantly increased the concentration of SOM in the topsoil, but also further affected humic acids (HA) optical and pyrolysis characteristics through changing the composition and structure of SOM. At 0-10 cm, the greatest SOM content was in CTW, but declined sharply with depth, while in DTF, DTW and CTF was not as high at the surface as in CTW, but the SOM content did not decline as fast as in CTW. The oxidation stabilization of SOM was generally greater in no tillage and ridge culture than that of disk till. The HA optical density in CTW at wavelength 665 nm and 465 nm was 0.122 and 0.705, while in DTF was 0062 and 0.321, respectively. E4/E6 ratios in CTW were higher than that of in the other treatments. The enthalpy capacity of exothermal peak (360-365 ℃) for HA DTA curve in no tillage and ridge culture was lower than that of in disk till, while the HA absorption peaks in 1000-1050 cm-1 presented the reverse trend. The oxidation stabilization coefficient of HA in no tillage and ridge culture was higher than those in disk till, indicating that polycondensation degree and aromatization of HA were stronger. Those findings suggest that it may be possible to manipulate paddy soils through conservational tillage and crop practices and thereby maintain adequate SOM concentrations, mitigate soil organic carbon loss from soil to atmosphere.