Abstract: In this paper, it detailed the characteristics, working principle, and pin functions of step-down DC-DC regulator LM5008A in power block of multi-parameter sensor, and introduced the application of LM5008A in multi-parameter sensor. It designed the peripheral circuits of LM5008A from the actual situation and the actual requirements, which made LM5008A maximize its function in multi-parameter sensor, and further ensured the overall performance of the multi-parameter sensor.