To study machining accuracy of NC machine tool,taking a four shaft polishing platform with floating platform and rotary platform as the research object,comprehensive geometric and thermal error modeling was carried out.XL-80 laser interferometer,PT100 temperature sensor and XSR90 color paperless recorded instrument were used to measure and record the temperature,position error of X,Z axis.The law between the positioning error of the moving axes and the temperature was studied.The geometric error model and thermal error model of X and Z axes were established by using Chebyshev polynomial and least square method respectively.The two models were superimposed to obtain the comprehensive positioning error model of X and Z axes of the machine tool,and the comparison between the fitting values of positioning error of X and Z axes and the experimental measurement values was conducted.The results show that the built model has characteristic of high prediction accuracy and good robustness.