The invention relates to a preparation process of 2-isopropylthioxanthone of light trigger, in particular to a process for preparing 2-isopropylthioxanthone by using 4-isopropylbenzenethiol and 2-chlorobenzoic acid as the main raw material through the reaction steps of condensation, exsolution, neutralization, cyclization, hydrolyzation, recrystallization, and the like. The preparation process is characterized in that the 4-isopropylbenzenethiol and the 2-chlorobenzoic acid are used as the raw materials and are condensed by using tetraline as solvent under the alkaline (lithium hydroxide) condition, the mol ratio of the 4-isopropylbenzenethiol, the 2-chlorobenzoic acid and the lithium hydroxide is 1:1-1.5:2-2.5, and preference for 1:1.05:2.1; the condensation temperature is 180-190 DEG C, the product is prepared by the reaction steps of exsolution, neutralization, cyclization, hydrolyzation, recrystallization, and the like after the reaction is performed for 6h. The invention has easily obtained raw materials, can improve the performability of the process, can greatly lower the production cost because the produced lithium hydroxide of the side product can be sold through the treatment and has high purity of produced products without isomer.