To address the high sensitivity measurement requirement of the test mass’s displacement in spaceborne gravitational wave detection, a ground-based simulation system using laser heterodyne interferometry has been established, initiating research into picometer-level displacement measurement techniques. Initially, the translational sensitivity of the designed laser heterodyne interferometer is tested under vacuum conditions. Subsequently, based on the sensitivity outcomes, noise source tracing research for the laser heterodyne interferometric system is conducted, including the development of a system noise model, analysis of various noise source mechanisms, and investigation of strategies to reduce the predominant noise sources. Ultimately, upon completion of the noise source tracing, the interferometric system is optimized, with tests indicating a displacement measurement sensitivity better than 1 pm/Hz^1/2 in the range of 30 mHz to 1 Hz. This paper is expected to provide a reliable ground-based test platform for noise source tracing, facilitating the advancement of picometer-level laser interferometry technologies for spaceborne gravitational wave detection.