Abstract: The non-asbestos fiber (NAF) cement flat sheet was used as the standard value sample for the test of architectural coatings, and the source of measurement uncertainty of non-asbestos fiber cement flat sheet was analyzed. The results show that the main factors affecting the uncertainty in measurement of NAF cement flat sheet reference material included sample homogeneity and the repeatability of determined values at different laboratories. The results were validated by F-test statistical method and showed that the homogeneity of the samples was good. The results of long term stability validated by t-test statistical method was 3 years. A cooperative certification test was conducted by 8 laboratories. Meanwhile,the uncertainty (k=2) was evaluated as surface smoothness of (0.08±0.05) mm, apparent density of (1.54±0.01)×10³ kg ·m^-3 and the water absorption rate of (23.7±0.3)%.