After using plated CBN hard gear-honing-tools with standard involute tooth profiles, there will be the middle concave errors generally around pitch circle on the machined gear tooth surfaces. For the factors caused to errors are much complicated, it is difficult to calculate them accurately by the analytic method. Therefore, Using Pro/E and ANSYS software, the engaging situation between gear-honing-tool and gear was simulated and analyzed. Based on the results of the analysis, the abrupt changing extent of the compression stress was determined near pitch circle. Along the number of the machined gear teeth was changed, the abrupt changing extent of the compression stress was varied accordingly, which was also coincided with the middle concave errors. Those provided the theoretical foundation for the tooth profile modification of the hard gear-honing-tools, it was proved useful to reduce or eliminate middle concave error in practice.