：By breaking through the limit of noncircular pitch curves of noncircular gears,a transmission mechanism comprised of a spur gear and a noncircular face gear is presented to achieve integrated transmission with speed reduction and change function,which could simplify the structure,save the space and improve the efficiency of the conventional speed reduction and change device to the most degree. A concept using noncircular curve instead of the pitch circle of normal face gear is proposed. According to the principle of pure rolling between pitch curves of two gears,the pitch curve formulae of the cylinder gear is deduced to reveal the transmission mechanism of the new gear set. Dividing the transmission ratio of the gear set into variable speed ratio and reduction ratio,the correspondences of the geometrical parameters and the two kinds of transmission ratio are built to realize any continuously variable speed rule. Based on the spatial meshing principle of gears,the tooth surface model of the noncircular face gear is deduced to provide theoretical basis for analysis of strength and geometrical characteristic. The transmission ratio of the noncircular face gear is calculated under different geometrical parameters,with some special advantages summarized. On the basis of digital simulation technology,the machining process of the noncircular face gear generated by a shaper cutter is given. The simulation tooth coincides with that by mathematical model,which verifies the correctness of the transmission theory of the new gear set.