A synthetic method of a novel visible light photocatalyst Bi2MoO6 (bismuth molybdate) is provided. The method includes the following steps: weighing Bi(NO3)3*5H2O and (NH4)6Mo7O24*4H2O solids at the theoretical ratio by mass of 14:1, dispersing the weighed solids into an appropriate amount of deionized water, stirring to obtain white curdy precipitates, placing the precipitates in a magnetic stirrer and stirring at normal temperature for 30 minutes, subjecting to ultrasonic treatment with a ultrasonic generator for 30 minutes to allow intensively mixing, allowing reactions of the treated white precipitates at 150-200 DEG C under sealed conditions, filtering the reaction product to collect flavescent precipitates, washing, drying, and grinding to obtain Bi2MoO6 (bismuth molybdate) photocatalyst. The photocatalyst has good photodegradation effect on target pollutants; and when the temperature of hydrothermal synthesis is 160 DEG C, the removal rate of target pollutant 4BS after photodegradation for 90 minutes reaches 99.5%. The inventive synthetic method has the advantages of simple process and low requirement for equipment, and is suitable for the synthesis of highly-active visible light photocatalyst Bi2MoO6 (bismuth molybdate).