The purpose of this study is to suppress the problem of vibration which occurs in a running two-cylinder reciprocating compressor. Determining an optimal crankshaft counterweight and narrowing the trajectory orbit of the crankshaft connecting rod mechanism is achieved. Use of finite element software (ANSYS) was used to simulate the modality of the two cylinders. In additions, the inertial force influenced to the crankshaft under different counterweight design was simulated. Simulation results by using SolidWorks software show the new counterweight was able to reduce the crankshaft's eccentric by 4mm and the orbit trajectory by 10mm. This study provides the procedures pertaining to the bettering performance and assessment for an existing reciprocating compressor.