The utility model relates to a self-contained corrosion potential measuring instrument under an ocean platform. The instrument comprises a gun-type bearing shell, wherein a potential measurement probe with electrodes is arranged at the front protruding part of the shell, a system packaging region is arranged at the rear cylinder part of the shell, and the system packaging region comprises a signal transmission cable and a signal processing system. The self-contained corrosion potential measuring instrument disclosed by the utility model has the following advantages: 1. potential measurement is implemented by double electrodes, namely an Ag/AgCl electrode and a Zn electrode, and the measurement results are shown by LEDs (Light Emitting Diode), thus increasing the amount of information acquisition in every operation, facilitating data analysis and enhancing the measurement reliability; 2. the measuring instrument has the functions of stationary recognition, automatic data storage and batched import, so as to lead to more convenient and simpler underwater operation of diver and better availability of data; 3. the measuring instrument adopting such a flexible design meets the demand of working both in a tethered mode and in a self-contained mode, i.e., the measuring instrument can not only be operated by diver, but can also be integrated with large equipment to get into water; and 4. self-luminous LED display can well satisfy the requirement on reading in a muddy water environment.