Abstract: In order to further improve the parameter reliability of the injection falloff test with the open hole wells in the low pressure and low permeability coal reservoir, with the analysis on the technique present status and theory of the domestic great injection falloff tests in the low pressure and low permeability coalbed methane wells, the paper held that the insufficiency of the test time was the important cause to occur the unreliable test results from the low pressure and low permeability reservoir. With the exchanged technique of the injection falloff test and the rational and effective prolonged well closed time, the reliability of the test results was improved. The study showed that there were potential dangers of the well accidents existed in the open hole wells. The well test time was limited and the casing well was not restricted by the test time. There were many advantages existed. According to the features of the low pressure and low permeability coal reservoir, the injection time was ranging from 8～12 h and the rational well closed time was 7～11 times higher than the injection time. The site application of over 30 coalbed methane parameter wells in Lu’an Mining Area,which showed the technical test result reliability of the extending time injection falloff tests in the casing wells.