The invention provides a voltage estimation method for power flow approximate calculation of a power system. The method comprises: step 1, performing direct-current power flow calculation on a grid to obtain a voltage phase angle theta of each node in the grid and active power Pbranch of each branch; step 2, constructing a grid equivalent model, and establishing a voltage estimation equation according to the model; and step 3, performing iterative calculation on the voltage estimation equation to obtain a voltage estimation result. Compared with the prior art, the voltage estimation method for power flow approximate calculation of the power system overcomes the defect that only the active power and the node voltage phase angle can be estimated by the direct-current power flow calculation, reserves the advantages of high speed and no convergence of the direct-current power flow calculation, and can estimate reactive power and node voltage amplitude based on the direct-current power flow calculation result, thereby comprehensively realizing power flow approximate calculation of the power system.