The hydraulic calculation of drip irrigation submain units plays a key role in the system design. The finite element method with virtual emitters can compute the head loss of each submain and capillary. The ways to reduce computational errors were suggested by selecting a certain amounts of elements in order to meet drip irrigation design need. Moreover, finite element method with virtual emitters can reduce computational work and memory demands dramatically. The research method put forward in this study provides a new way for hydraulic design of large drip irrigation system.