Aiming at the optimal selection problem of drip irrigation mode under plastic mulch, the paper started from the set pair analysis (SPA),and calculated and analyzed the relational degrees between evaluation mode and the optimal mode, intermediate mode and worst mode by the gray relation (GR) analysis. It built the connection degree formula of model evaluation of drip irrigation under plastic mulch，and realized the evaluation for many irrigation modes. This model was applied to evaluate nine kinds of drip irrigation under plastic mulch.The irrigation mode 4 is the most optimal. Namely, the seedling irrigation time delays 2 days than the control mode, full water is supplied during bud stage, and that proper control of water is supplied at the early and later flower stage. The result showed that catastrophe theory and projection pursuit accords with the field test recommended irrigation mode. This shows that the method can objectively and truly reflect the evaluation problem of drip irrigation under plastic mulch.The evaluation result is reliable.