According to the test method of the water permeability of synthetic resinemulsion coatings for exterior wall，which was specified in the national standard GB/T 9755— 2014“Synthetic Resin Emulsion Coatings for Exterior Wall”，the influential factors of the substrate on the water permeability test were studied and analyzed. By comparing the waterpermeability test results of non-asbestos fiber cement sheet from different manufacturers，the results showed that the performance parameters of the test sheet had an impact on the waterpermeability of the empty board and the coating. Test the changes in the water permeability ofthe coating film after adding different putty layers to the sheet，and the results showed that the putty layer had an impact on the water permeability of the coating film. Compared theinfluence of large-capacity funnel and national standard test funnel on the water permeability.The results showed that large-capacity funnel had a shielding effect on the substratedifferences in the water permeability test.