The piston-cylinder part is the core component for the function realization of the aviation piston pump, and the power to weight ratio is an important index of the piston pump. Improving the power to weight ratio of the piston pump according to lightweight design of the piston pump is the development trend of the aviation pump. Aiming at the high proportion of cylinder mass in the piston-cylinder parts of aviation piston pump, the bimetal cylinder block was lightweight designed. The kinematic analysis of the piston-cylinder block was carried out, and the load distribution of the piston-cylinder block was obtained. The finite element models of the single/bimetal piston block before and after lightweight design were built, then the strength and stiffness of these structures were calculated respectively. The results show that the bimetal piston block can meet the normal working requirements of aviation piston pump, and in the condition of ensuring the strength and stiffness of the cylinder block, the outer diameter of the cylinder block after lightweight design can be reduced by 4.4%, and the whole weight can be reduced by 14.42%.