The traditional synthesis method of triisobutyl phosphate was improved, and phosphorus oxychloride and excess isobutanol were used as raw materials to synthesize triisobutyl phosphate by one-step method. The optimal process conditions were determined by experiments: n(oxytrichloride) Phosphorus): n (isobutanol)=1:7, dropping temperature: 0～10℃, holding temperature 30～35℃, vacuum degree: 0.09～0.1 MPa, product yield 88%, content > 99.0%, The distillation residue was green treated.