The present invention relates to the compound [4-(2-amino-10-methyl-4-oxo-6,7,8,9-tetrahydro-4a,7-cycloimino-pyrimido[4,5-b] [1,4] diazepine-5(4H)-yl)benzoyl]-glutamate (JK12A for short) with the structure of Formula I. The present invention also relates to the crystal form and salt of the compound JK12A, and preparation methods and applications thereof The compound JK12A of the present invention can be used to prepare drugs as an active ingredient for medicaments or food additives.