Abstract: In this paper, the effects of atmospheric pressure on the test result of desorbed coalbed gas content were studied. It is indicated that after samples returned to laboratory of higher atmospheric pressure from sampling site of lower atmospheric pressure, the desorbed gas content decreased obviously of every 24h.For samples that the desorbed gas content is zero or very little during the first seven days and the test should be ended according to the standards, the test duration should be extended to about 3 weeks. If the desorption test is conducted at the sampling site until the end, the total desorbed gas content will be higher than that in the laboratory.