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As the basic unit of complex transmission,two-row parallel planetary gear mechanism needs to be considered as whole in transmission ratio computation. According to the design requirements of vehicle automatic transmission,the design procedure for two-row parallel planetary gear mechanism is proposed based on the lever method using 3-node unified single-row single-stage and two-stage model,and the principle are illustrated by diagram. A new type of two-row parallel planetary gear mechanism（ single-stage and two-stage CC-SS） is designed and compared with the classical transmission A341 E（ single-stage and single-stage CR-SS）,4 T65 E（ single-stage and single-stage CR-RC）,AG4（ single-stage and single-stage CC-RR） and the transmission（ different case of single-stage and two-stage CC-SS） from a certain car,results show the new type of gear mechanism overall has obvious advantages of larger transmission ratio range,small transmission ratio step and least shifting components.

According to the characteristics and requirements of automatic transmission planetary gear,taking equal or close strength as optimization objective,optimization model of considering to minimize gear contact fatigue stress difference and bending fatigue stress difference is built under 40 constraint conditions including keeping reasonable transmission ratio,volume decrease,etc. And optimization calculation is performed by using MATLAB. Compared to the original design,the maximum value of planetary gear contact fatigue stress and bending fatigue stress,stress difference and integral stress decrease after optimization,especially the maximum value of bending fatigue stress decrease 12. 24% and all gears root bending fatigue stress are almost the same,the optimization effects are significant. The volume of optimized planetary gear mechanism is 3. 54%smaller than the original design,and the optimal design is superior in transmission ratio,dimension and processing parameters.

According to the design requirements and characters of mining truck,an optimum mathematical model of transmission is set up to maximize actual power under the precondition of reliability. The transmission of mining truck is optimized by using optimization toolbox of MATLAB. With the visual display of the optimum results,several performance indexes such as the driving force,stand-by power and actual power are compared with the original design and among the optimum model,thus can provide an alternative option. Compared with original design,a good optimization effect is obtained from the optimum model of transmission.