The present invention discloses a crystal of citrate salt of pyridine-substituted 2-aminopyridine-based protein kinase inhibitors, in particular, to crystal of 5-((R)-1-(2, 6-dichloro-3-fluorophenyl)ethoxy)-4' -methoxy-6' -((S)-2-methylpiperazin -1-yl)-3, 3' -bipyridin-6-amine citrate salt, a method for preparation thereof, a crystalline composition and a pharmaceutical composition comprising the crystal, and further discloses the use of crystals of citrate salt of the compound of Formula I in protein kinase-related diseases. The crystals of citrate salt according to the present invention are superior to 5-((R)-1-(2, 6-dichloro-3-fluorophenyl)ethoxy)-4' -methoxy-6' -((S)-2-methylpiperazin-1-yl)-3, 3' -bipyridin-6-amine or other salts of 5-((R)-1-(2, 6-dichloro-3-fluorophenyl)ethoxy)-4' -methoxy-6' -((S)-2-methylpiperazin-1-yl)-3, 3' -bipyridin-6-amine in at least one aspect of bioavailability, hygroscopicity, stability, solubility, purity, ease of preparation, and the like.