Abstract: Baryon numbers are absolutely conserved in the standard model. However, according to the grand unified theory, nucleons in the nucleus will decay and baryon-number conservation may not be absolute. In this paper, the physical concepts, detection, and experimental status of nucleon decay research are reviewed. Our proposals to improve experimental methods and techniques are also presented. Up to now, the proton lifetime τp is deemed to be greater than 1032 years. The detection of nucleon decays will be very helpful for validation of new theoretical models and the development of cosmography and particle physics.