The introduction of heteroatoms into manganese dioxide (MnO2) is an effective method to adjust the active site of electrochemical water oxidation catalysis. Although many modification methods for MnO2 have been studied in electrocatalytic oxygen evolution reaction (OER), few studies have focused on the influence of regulating different crystal forms of MnO2 on catalytic activity. This article prepared four different crystal forms of MnO2 (α-MnO2, β-MnO2, γ-MnO2 and δ-MnO2), and systematically studied the catalytic performance of the catalyst (x-MnO2-Ru) prepared by adding Ru to α-MnO2, β-MnO2, γ-MnO2 and δ-MnO2 for OER. The results of linear sweep voltammetry and chronopotentiometry measurements show that the catalyst prepared by adding Ru to β-MnO2 (β-MnO2-Ru) has the best electrochemical performance. β-MnO2-Ru shows a low overpotential (300 mV at 10 mA·cm-2) and outstanding catalytic activity with small degradation after 24 h operation. It is found that β-MnO2-Ru exhibits excellent electrocatalytic performance due to its abundance of Mn3+and defect oxygen vacancies.