Provided is a prefabricated construction method for a prestressed concrete box girder. Firstly, a prefabricated girder field is constructed; a prefabricated pedestal is manufactured in a prefabricated area; a lateral mold is erected on the pedestal; a steel reinforcement framework is put into the lateral mold; an inner mold and an end mold are installed; then concrete pouring and concrete maintenance are conducted; after the intensity of the concrete reaches 90% of the designed intensity and the maintenance time is longer than 7 days, prestress tension and grouting of a pore canal are conducted; and after the intensity of a grouting test block in the box girder pore canal reaches 90% of the designed value, the grouting test block is moved to a girder storage area. Steel reinforcement machining is conducted through a numerical control steel reinforcement bending machine, so that the machining precision and efficacy of steel reinforcement are improved; an automatic spraying and maintaining system is adopted, so that accuracy of maintenance time and reliability of maintenance quality are ensured; an intelligent tensioning and grouting system is adopted, so that automation and refinement of tensioning and grouting are achieved; a sliding contact line power supply system is adopted, so that power use safety is ensured. The standardization, factorization, intelligence, refinement and automation of the prefabricated construction method for the prestressed concrete box girder are achieved.