To guarantee the accuracy of error analysis and evaluate the manufacturing tolerances influence, a numerical error analysis method for parallel kinematic machines (PKMs) is presented in this paper. Quasi-Newton method and genetic algorithm are introduced for the forward kinematic solution. Based on the inverse and forward kinematic solutions, the end-effectors error calculation procedure is developed. To solve the accuracy problem caused by the length and angular parameters different units, a normalization method is proposed based on the manufacturing tolerance. Comparison between the error analysis results calculated by the traditional method and the numerical method for a 4RRR PKM shows that, this numerical error analysis method is more accurate, simpler, and can evaluate the machines real error based on the manufacturing tolerance.