Thickening time control agent used for gypsum mortar, and preparation method thereof

The invention relates to an additive of gypsum mortar and a preparation method of the additive, and more specifically discloses a thickening time control agent used for gypsum mortar. The thickening time control agent comprises following ingredients, by weight, 23 to 27% of anhydrous citric acid, 18 to 22% of anhydrous sodium pyrophosphate, 7 to 8% of hydroxy propyl methyl cellulose ether, 4.5 to 5.5% of sodium tripolyphosphate, 9 to 11% of pregelatinized starch, 18 to 22% of sodium bentonite, 9 to 11% of polycarboxylate superplasticizer and 2.2 to 2.8% of inorganic aluminum magnesium silicate gel. The thickening time control agent is added into gypsum mortar which is prepared by taking desulfurated gypsum powder as a gelling material, so that thickening time of gypsum mortar can be adjusted by adjustment of the amount of the thickening time control agent according to the difference of construction environment and temperature, and operation time can be prolonged appropriately according to requirements.