By studying the method of flow coefficient stability control of valve hole in aero-engine control system, a set of algorithms for transforming the square hole into small circular holes with regular arrangement were proposed. The correctness of the algorithm was verified by an example, and the conversion error was less than 0.7%, which basically realized the constant flow coefficient in engineering sense. The algorithm converted the square holes with poor machining process and low measurement accuracy into small round holes with regular arrangement and combination. So the influence of changes in flow coefficient caused by square holes was eliminated, the processing method of the valve hole was changed, the hazards to people and the environment were reduced, the measurement precision of the valve hole was improved, and the hydraulic power of the valve was reduced, presenting great engineering application value. The algorithm can transform the square, trapezoid (including triangle) and its combined holes, showing universal applicability in engineering.