The turning process is a complex dynamic material removal process that is influenced by many linear and nonlinear factors. Meanwhile, it is not easy to measure complex free-form workpieces through the CMM (Coordinate Measuring Machine). Hence, machining simulation is an essential method to evaluate the performance of the NC system. This article proposes a novel machining surface topography generation algorithm that directly calculates data according to the actual tool trajectory (including tool’s position and attitude angle) and cutting tool contour. Especially, take three specific tool’s deviation situations into account to increase the completeness of this algorithm in reality. Finally, through comparative simulation to illustrate the advantage and precision of this algorithm. The simulation results show that the calculation error is no more than 12.5 nm. It is suitable for application in evaluating the performance of NC system to machine free-form workpieces.