Abstract: A remote online self-checking unit based on charge signal is designed to provide a fast and effective remote online self-checking method for the primary instrument of the Loose Parts Monitoring System (LPMS) installed in the reactor building of the nuclear power plant. The design principle and the method of the remote online self-checking unit, as well as the hardware design and software flow design are introduced. A laboratory test is conducted on the remote online self-checking unit, and the test result shows that the remote self-checking unit can meet the requirements of 250 m under the condition of no-load output 5 V voltage. Meanwhile, the domestic LPMS prototype integrated with the remote online self-checking unit is verified to meet the engineering application environment through the qualification test. Two sets of the domestic LPMS products integrated with the remote online self-checking units have been successfully applied in the C-3/C-4 unit of the Chashma Nuclear Power Plant in Pakistan. With low cost and high efficiency, the online self-checking function of LPMS primary instrument during the reactor loading operation is realized.