The Piston compressor is a positive displacement compressor with crankshaft, connecting rod, crankcase, piston etc. as main components. Piston compressor are highly used in oil and gas industries as they demand high pressure air, also chemical, petrochemical and process gas plant use piston compressor for compressing final product gases. This compressor used at CNG stations to refill the automobile CNG tanks. The crankcase is the core structure of the reciprocating compressor, supports and encloses almost all internal components of piston compressor. The main function of the compressor crankcase is to provide sufficient rigidity to the compression mechanism to make it work properly. Another function of the crankcase is to act as a limiter that absorbs any shock that may occur during compressor transport. Crankcase is one of the bulky part in piston compressor and there persist the scope of weight reduction of crankcase. This paper focus on static and harmonic analysis of crankcase . For doing analysis of crankcase along with crankcase crankshaft, connecting rod, crosshead guide, cross head also weight of cylinder and piston are considered. For analysis purpose FEA solver (ANSYS) is used. static analysis is done to check stresses in crankcase, harmonic analysis is done to evaluates vibrations in terms of velocity. After transient dynamic analysis By analysing the results optimization of crankcase will be done for weight reduction.