The compressor blades from class 4 to class 6 in a certain type of engine are taken as the objects of study. Based on the standard ground atmosphere and the aerodynamic parameters such as the pressure, the temperature and the velocity calculated under the condition of the design rotating velocity and with the blade twist law being unknown, the aerodynamic loads borne by the rotating blades are calculated approximately. During the calculation, the energy conversion relations in the course of compressor pressurizing and the expression of stage compression work are used, the fact that the loads borne by the rotating blades are far greater than those borne by the static blades and simultaneously the fact that the breakdown rates of the rotating blades are much greater than those of the static blades are all taken into consideration. In this paper the changes of the aerodynamic loads of blades class 4 to class 6 with the blade height under the condition of the designed rotating speed of the engine are calculated approximately, thus an approximate calculating method for calculating blade aerodynamic load is found, which lays the foundation for the strength checking and the vibration analysis.