To improve the dynamic accuracy of a five-axis machine tool, an evaluation method based on a test piece and a comprehensive evaluation (CE) system is proposed in this paper. The test pieces, namely, cone frustum and S test piece, in ISO 10791-7 are compared to show their ability to reflect the dynamic accuracy. After the comparison, the S test piece is selected owing to its various changes in contour error under different dynamic accuracies. The kinematic and dynamic simulation model is established to affect the effects of the various dynamic factors on the S test piece. The relationship between the dynamic factors and the S test piece is applied to the construction of a CE system. Then, the evaluation of the dynamic accuracy of the five-axis machine tool can be completed. On the basis of the evaluation result, the error is identified to determine the factors that must be adjusted. Thus, the dynamic accuracy of the five-axis machine tool can be improved by the adjustment. The proposed method is validated by experiments.