Abstract: In order to improve the surface quality of low temperature co-fired ceramic (LTCC) substrate in multi-chip module (MCM-C/D) technology, it is necessary to use chemical mechanical polishing (CMP) process to flatten the substrate surface. This paper discusses the optimization design method of substrate CMP process parameters based on Taguchi test method. Under certain polishing conditions, pH value of polishing slurry, polishing load and rotation rate of platen are the main process parameters that affect the surface quality of substrate. Experiment with three factors and three levels is designed to study these parameters. The results show that the factors affecting the CMP planarization of substrate surface are polishing load, pH value of polishing slurry and rotation rate of platen in sequence. The optimized parameters are adopted to obtain a smooth and flat surface with the substrate roughness R_a ≤ 0.05μm and the bulging height H ≤ 3μm, which meets the application requirements of thick and thin film hybrid substrate after the validation of film process.