A digital design method of non-circular gears based on target transmission ratios was proposed.The discrete point sets on the pitch curve of driver gear and passive gear were calculated by using differential geometry,the outline of pitch curve was fitted by using cubic spline; according to the generation method,cutter envelope graph was obtained,after the tooth profile curve was extracted,a certain tooth width was given to obtain the 3D model of the non-circular gear; the motion simulation was carried out after assembling the driver gear and passive gear model; the dynamic interference check was carried out in the transmission process,and the theoretical value and simulation value of angular velocity response curve of driven wheel were compared to verify the correctness of the model.The results show that it is feasible to use this method to design non-circular gears,which can promote the subsequent analysis,manufacturing and other work.