Abstract: For the impact of capillary import pressure, import status, and structural changes on capillary flow, this paper proposed a new fast calculation formula. The formula has the explicit form, in which does not exist iteration, and it guarantees highspeed and absolute stability of the flow calculation. When the back pressure is given, the export flow can be judged whether it is a critical flow. Software is used to check point from the ASHER Handbook nomogram and a verification is given. The result shows that the average relative deviation is 2.17%, the largest relative deviation is 13.42%, the result is ideal. At the same time, the influence of the capillary diameter, length, and import status on the capillary flow is analyzed. The model can be used in capillary flow calculation model directly.