Abstract: Blowout preventer (BOP) is installed on subsea wellhead during the normal drilling operation of the semi-submersible drilling platform. Main functions of BOP are achieved by the integrated operation of the surface control system, hydraulic transmission system and subsea control valve manifolds (control boxes). The blue/yellow box control units serve as mutual backups. Each unit is composed of HKR (hydraulic pressure regulating) valve, SPM (hydraulic control two-position two-way) valve, hydraulic pipe and joint. Currently, the control system uses a large number of SPM valves, resulting in high maintenance costs. In order to reduce failure rate and maintenance cost of SPM valve, it is essential to realize the localization of these valves. This paper analyzes the structure and function of two types of SPM valves, and presents their application scenarios, advantages, disadvantages, failure points and proposes targeted maintenance methods and localization considerations for the spring-reset SPM valve. The conclusions of this study contribute to promoting and ultimately completing the localization of SPM valves.