The invention discloses a form A of mesylate for nicotinamide derivatives and preparation method and application thereof, wherein the XRPD pattern of the form A of mesylate for nicotinamide derivatives has a diffraction peak at 2θ=5.34, 10.341, 14.438, 15.841, 17.32, 18.301, 18.68, 19.005, 19.577, 20.26, 21.161, 21.859, 22.379, 23.04, 23.5, 24.177, 24.959, 25.881, 26.641, 27.18, 28.3, 28.999, 29.501, 31.96, 32.258, 33.999, 36.798, 37.38 and 41.297 with the error range of the 2θ values being ±0.2. The form A of mesylate for nicotinamide derivatives provided by the present invention has excellent high-temperature stability, high-humidity stability and illumination stability, and it can be applied to drugs for treating advanced non-small cell lung cancers, gastric cancers, liver cancer or breast cancer. It has preferable bioavailability, and meanwhile the provided qualitative and quantitative information has great significance on further study of the efficacy of such solid drugs.
