In order to study the effect of trappedoil pressure on lubrication state of journal bearing in external gear pumps,a formula for calculating the needed loadcarrying factors between bearing and journal based on the design requirements of all fluid lubrication state was established.A polynomial formula of provided loadcarrying factors by a prototype of a gear pump was fitted based the parameters of the prototype by Excel software.Through the zero value solution of the needed loadcarrying factors minus the provided loadcarrying factors tby the programming solver of Excel software,the corresponding relationship between the trappedoil pressure and the minimum oil film thickness on journal bearing was derived.The lubrication state of the journal bearing of a prototype of a gear pump was studied when considering and not considering the trappedoil pressure.The results of the prototype show that the trappedoil pressure causes the increasing of the radial force from 45% to 59%,and the decreasing of the minimum oil film thickness from 19.6% to 24.3%.The journal bearing is in mixed lubrication state because of the effect of trappedoil pressure,which can not meet the original design requirements of all fluid lubrication state.It is concluded that the oil trapping pressure has a great influence on the lubrication condition,the influence of oil trapping pressure should be fully considered in the design of pump shaft,so as to alleviate the oil trapping pressure as far as possible in structure.