The invention discloses a preparation method and an application of a highly crystallized 
carbon nitride photocatalytic material, and belongs to the technical field of 
semiconductor photocatalytic materials. The method comprises the following steps: 1) calcining 
melamine in a 
muffle furnace to obtain a heptazine precursor; 2) 
grinding and uniformly mixing the heptazine precursor, 
potassium salt andlithium salt, and calcining the mixture in the 
muffle furnace; 3) taking out the calcined product, and cleaning and 
drying the calcined product to obtain crystallized 
carbon nitride; and 4) dispersing the obtained crystallized 
carbon nitride in 
hydrochloric acid, continuously stirring the 
system, and finally washing and 
drying the 
system to obtain the highly crystallized carbon 
nitride photocatalytic material. In the invention, the crystallized carbon 
nitride is treated in the 
hydrochloric acid aqueous solution, so that the 
crystallinity of the obtained carbon 
nitride is greatly enhanced. Thehigh-
crystallinity carbon nitride has great advantages in the aspects of photo-generated carrier migration and photo-generated 
electron hole pair inhibition. Meanwhile, 
potassium ions embedded into the high-
crystallization carbon nitride middle layer make great contribution to migration of photo-induced electrons. Based on the two characteristics, the photocatalytic 
hydrogen production activity of the high-crystalline carbon nitride is greatly enhanced.