Copper(I) thiocyanate (CuSCN) is a p-type semiconductor with exceptional properties for optoelectronic devices such as solar cells, thin-film transistors , organic light-emitting diodes, etc. Understanding the structure-optical property relationships in CuSCN is critical for its optoelectronic applications. Herein, high-pressure techniques combined with theoretical calculations are used to thoroughly investigate the structural and optical changes of CuSCN upon compression. Under high pressure, CuSCN exhibits a progressive decrease of the band gap with different rates, which is relevant to the β to α phase transition in CuSCN and the subsequent amorphization through polymerization. UV-vis spectra measurements reveal a reduction in band gap from 3.4 to 1.3 eV upon decompression to ambient conditions. Such transitions could be attributed to the pressure-induced rotation of CuNS3 tetrahedron and bond length shrinkage. The severe distortion of the polyhedral units prompts breakdown of the structure and thus the amorphization, which is quenchable to ambient conditions. Our study demonstrates that high pressure can be utilized to adjust the structure and optical characteristics of CuSCN compound, potentially extending the material's uses in optoelectronic devices.