Disclosed are a p-toluenesulfonate of a MEK kinase inhibitor, and a crystal form thereof and a preparation method thereof. Specifically disclosed are a 2-((2-fluorine-4-iodophenyl)amino)-1-methyl-4-((6-methylpyridine-3-group)oxygroup)-6-carbonyl-1, 6-dihydropyridine-3-formamide p-toluenesulfonate (a compound represented by formula (I)), a crystal form I, and a preparation method thereof. The obtained crystal form I of the compound of formula (I) has good crystal form stability and chemical stability, and the crystallization solvent used has low toxicity and low residue, and is more suitable for use in clinical treatment.