Abstract: The key issue arising from digitalization of the reactor protection system for nuclear power plant is how to carry out verification and validation (V&V), to demonstrate and confirm the software that performs reactor safety functions is safe and reliable. One of the most important processes for software V&V is unit testing, which verifies and validates the software coding based on concept design for consistency, correctness and completeness during software development. The paper shows a preliminary study on the technique for unit testing of safety software V&V, focusing on such aspects as how to confirm test completeness, how to establish test platform, how to develop test cases and how to carry out unit testing. The technique discussed here was successfully used in the work of unit testing on safety software of a digital reactor protection system.