The position errors in the axis direction of a vertical machine center have been measured using the VM101 linear encored measurement system which has made in HEIDENHAIN cooperation. The setup is simpler and the measurement process is less time consumer compared with the laser interferometer. The character of the backlash error is discussed, its effects on the machine accuracy is presented. Results show that the backlash error has great influence on the position error. The error model for the soft error-compensation based on the Back Propagation Artificial Neural Network (BP-ANN) has developed. The position accuracy is enhanced after the backlash errors are compensated.