To fulfill the need of computer assistant decision-making and simulating battle drilling, based on the basic helicopter spot performance and a few of original data, the paper makes a model of the Algorithm of rotor's power. By analyzing the characteristics of dynamics and using the momentum theory and blade theory, a computational method of helicopter rotor power and available power is deduced. The rotor power will be respectively calculated as several parts. The pull's calculation model is established with the remnant power by using the linear outer insert method. Finally,a calculated example proves the feasibility of the simplified arithmetic model,thus the problems of flight performance assurance and dynamics simulation are solved.This algorithm is of applied importance.