High entropy oxides (HEOs) are often used for the oxygen evolution reaction (OER) due to their tunable electronic structure, variable composition and structural stability. However, the catalytic activity of conventional HEOs is limited due to their high crystallinity, resulting in a low number of active sites on the surface. Anion doping, on the other hand, is a method that can effectively increase OER activity. In this study, a series of P-doped HEOs were synthesized and the effect of P doped on HEOs was investigated. It was found that P doped increased the metal (Co, Ni, Mn)-oxygen covalency in HEOs and generated a large number of oxygen vacancies. The electrochemical properties of HEOs with different P doped levels were also compared, and HEO-P-1 showed the best catalytic performance, reaching a current density of 10 mA cm−2 at an overpotential of only 254 mV. Then, the surface reconstruction process of HEO-P-1 was also investigated and it was found that the (oxygen) hydroxides of Co-Ni-Mn play a real catalytic role. Finally, the OER mechanism catalyzed by HEO-P-1 was investigated. This work provides a new idea for effective doping of anions in HEOs for efficient OER catalysis.