Abstract: In allusion to the calculation method on the discharge head of pump at two-phase flow, this paper carries out a calculation on the assumption that both gas phase and liquid phase has itself velocity, no energy transports between them, but maybe mass transfers, so that, the discharge head provided to fluid by pump can be divided into two parts, that is, one is provided to the liquid, and the other is provided to gas. Meantime assumed that, the variation of the fluid within the inlet and outlet of pump is a isothermal process. About the calculation on the discharge head provided to gas by pump, the paper presents three kinds of calculation methods, analyzes and compares the case calculation results.