The invention discloses a manufacturing method for a prestress small box girder. The prestress small box girder is divided into an open groove section located in the middle and anchoring sections located at the two ends, the manufacturing method comprises the following steps that 1, the open groove section is poured, open grooves used for arranging prestress ribs are reserved in a web plate of the open groove section, and two tensioning holes used for tensioning the prestress ribs are preset at intervals for a certain distance at the bottoms of the open grooves; 2, the prestress ribs penetrate through the open grooves reserved in the open groove section, the prestress ribs after penetrating are fixedly connected with steel bar cages of the anchoring sections at the two ends of the prestress small box girder, and the anchoring sections located at the two ends of the prestress small box girder are poured; 3, after the anchoring sections are poured and solidified, the prestress ribs aretensioned downwards by tensioning equipment through two transverse tensioning holes in the bottoms of the open grooves, and the tension value and the elongation value of the prestressed ribs are checked to meet the requirement; and 4, the open grooves in the open groove section are poured, then the third pouring is finished, the tensioning equipment is disassembled after the open grooves are solidified, and then the manufacturing of the whole prestress small box girder is completed. According to the manufacturing method for the prestress small box girder, the grouting in the prestressed tension of the small box girder is denser, and meanwhile, the utilization rate of the prestress ribs is improved.