A series of metal-organic framework (MOF) materials have been synthesized by the solvothermal method using trimellitic acid and terephthalic acid to react with nickel and cobalt metal salts for photodegradation of methylene blue (MB) under irradiation with a xenon light source. ML-3, a tight-flower structure synthesized on the basis of solid blocks structure NC-3, is a bimetallic mixed-ligand MOF material with a specific ratio, which has excellent degradation performance against MB. The degradation efficiency of NC-3 is 80.6% in 120 min, while the degradation efficiency of ML-3 can reach 97.8% in 120 min. The radical trapping experiments and Mott-Schottky analysis were carried out to reveal the photocatalytic degradation mechanism. The result showed that h⁺ and·O₂^– were the main active substances; while the redox potential of MB (1.77 eV) was lower than the valence band (VB) potential of ML-3 (2.01 eV), and h⁺ could directly oxidize MB. Therefore, the as-synthesized materials in this study are effective wastewater treatment agents and have a promising future in environmental treatment.