In order to investigate the response of seed germination and seedling growth of C3 and C4 plants to climate warming,authors regarded two herb species Stipa bungeana and Bothriochloa ischaemum as well as two small semishrub species Artemisia frigida and Kochia prostrate as objects,which are separately coexisting in Inner Mongolia steppe. OTC was designed to simulate warming to observe the seed emergence and seedling growth,biomass accumulation and allocation of four plants. The results showed that: (1) simulated warming significantly increased seed emergence percentage,emergence rate and decreased seedling mortality rate of C4 species(Bothriochloa ischaemum and Kochia prostrata) relative to C3 species(Stipa bungeana and Artemisia frigida) (P < 0. 05). (2) The seedling growth of different photosynthetic type responded to simulated warming differently: warming significantly increased the seedling height of C_3 plants(P < 0. 01) while the leaf length and leaf area of C_4 plants(P < 0. 05). (3) Simulated warming had little effect on biomass accumulation of C_3 seedlings but an obvious promotion of aboveground biomass accumulation of C_4 seedlings. (4) Warming increased the root biomass allocation of Artemisia frigida(C_3) (P < 0. 05),but had no effect on the biomass allocation of other three plants. Based on the results we can predict that the seed emergence and seedling growth of C_4 species will benefited from the air temperature rise of 2℃ in the future. The results can provide the basis for further research of the composition,distribution and adaptability of C_3 /C_4 species under climate change.