Abstract: The water discharge from CBM well is usually regarded as the water production from coalbed during dynamic analysis of this kind of wells. Based on wellbore storage effect, the paper analyzes the relationship between water discharge from wellbore and water production from coalbed, compares the 2 water productions with different working fluid levels, concludes that wellbore water discharge may not be equal to water production from coalbed and establishes a modified formula of coalbed water production. Then the calculation results of the production data from Well XX of TS well group, Qinshui basin show that there is an obvious gap between wellbore water discharge and coalbed water production during the first production stage with the peak value difference reaching 72% of wellbore water discharge; the maximum coalbed water production is 25% higher than the maximum wellbore water discharge due to sharp pressure variations at the second and third production stages. Meanwhile, the influence of the difference between wellbore water discharge and coalbed water production on production is simulated with a mechanism model and based on production data in Well XX of TS well group, Qinshui basin. The result shows: if the wellbore water discharge is considered to be equal to the coalbed water production, coal seam pressure drop rate will be accelerated, the gas breakthrough time will be 79 days in advance and the peak of gas production will be reached 180 days in advance as well. It is concluded that the water discharge from CBM well is not equal to the water production from coalbed when the pressure changes in the coal bed. Otherwise, dynamic analysis, production system determination and implementation and numerical simulation for CBM wells will be wrong