To quantify the population size of total methanogens changing with environments, season and depths of Zoige plateau, the plasmids and standard curves of species were constructed by using real - time absolute quantitative PCR. The concentration of the standard plasmids was 160 mg/L, with the coefficient being 0.992, and the amplification efficiency was 98.6%. The results showed that in April the population size of total methanogens in wetland ecosystem and grassland ecosystem were nearly the same. In wetland ecosystem, the population size of total methanogens decreased in the order of September, July, and April, while increased with the sampling depth in September and July, In grassland ecosystem, however, the population size of total methanogens did not change significantly with season and depth.