Abstract: In order to evaluate the energy consumption of pump operation under variable working conditions rationally, state graph of pump operation based on pump characteristic curve and flow rate variety curve has been established in three dimensions. A model to calculate the energy consumption index of pump operation under variable working conditions has been established, which can solve the problem of existent model. In the model, energy consumption of pump operation in a time-interval was calculate by a definite integral, product of water supply amount and head was calculate by a double integral. The energy consumption index of pump operation of a pump station was calculate by the model. The results showed that it can calculate the energy consumption of pump operation under variable working conditions rationally.