Abstract: In order to provide a reasonable basis for the rotational tillage system, the effects of different tillage practices on soil microbial biomass carbon (SMBC) were determined in double maturation of wheat-corn cropping fields with long-term non-tillage in North China Plain. The results showed that tillage managements significantly influenced spatio-temporal variations and stability of SMBC in long-term non-tillage soil. SMBC in the 0~5 cm and 5~10 cm soil layers exhibited obvious seasonal variations in different treatments. While the lowest value was at double ridge stage, the maximum was at harvest stage of wheat. In deep soil layers, there were insignificant seasonal variations in SMBC. SMBC significantly decreased (P<0.05) with soil depth under non-tillage and straw mulch (NT) treatment. In the 0~5 cm and 5~10 cm soil layers, SMBC was insignificantly different under conventional tillage (CT) and rotary tillage (RT). Among all other soil layers, however, SMBC was significantly different (P<0.05). Compared with NT treatment, CT and RT dropped average SMBC by 6.7% and 6.1% in the 0~5 cm layer. However, CT and RT significantly increased SMBC by 30.2% and 20.7% (P<0.01) in the 5~10 cm layer. Also average SMBC under RT and CT increased significantly by 10.5% (P<0.05) and 48.1% (P<0.01) in the 10~20 cm layer. The trend of the effects of different treatments on SMBC stability in the 0~20 cm soil layer was as follows: CT > RT > NT. That in the 20~30 cm soil layer was NT > CT > RT.