Based on the Boolean subtraction operation and curve fitting technology,a digital modeling method for variable ratio rack is put forward. This method,to a certain extent,makes up for the disadvantages that the Boolean subtraction operation modeling method is inaccuracy. According to the variable ratio curve,generating cutting process of the gear is simulated,and the variable ratio rack initial model are established based on Boolean subtraction operation. By extracting the approximation of the tooth profile point and fitting these tooth profile points with different number of polynomial,the variable ratio rack 3D model is generated by modeling software. The dynamic characteristic simulation analysis of the repaired variable ratio rack is carried out by different number of polynomial,with the aim to measure the dynamic transmission error percentage and acceleration of variable ratio gear pair. The effectiveness of this method is verified by the comparison analysis results.