The invention discloses a special coloring agent of a 
diammonium phosphate compound 
fertilizer, comprising the following constituents: 40-50 parts of 
humic acid salt, 0.1-3 parts of carbon 
soot, 2-4 parts of acid black, 1-2 parts of acid brilliant scarlet, 0.2-1 part of 
sodium hexametaphosphate, and 40-56.7 parts of water by weight parts; the preparation process is that: the material is prepared by weight parts, water is added in a vertical round reaction tank, and then the 
humic acid salt, the carbon 
soot, the acid black and the acid brilliant scarlet are added and are stirred uniformly, andthen 
sodium hexametaphosphate is added, the mixture is stirred continuously and uniformly, so as to obtain the special coloring agent of the 
diammonium phosphate compound 
fertilizer; the invention solves the problems that the 
diammonium phosphate particles produced under an acid 
slurry condition are easy to decolorize and the 
chromaticity is unstable; the special coloring agent of the diammonium 
phosphate compound 
fertilizer is green and environmental-protection, has no 
pollution and is beneficial to the growth of crops; the product is in a 
liquid state and transported closely, and has convenient usage; the 
raw material is cheap and easy to obtain, the cost is low and the economic benefit is good.