The invention relates to the technical field of assembly of engine oil pump parts, in particular to a rotary positioning mechanism and an oil pump assembly line. The rotary positioning mechanism can drive workpieces to rotate by a certain angle and is inserted into a positioning hole through a positioning shaft assembly to achieve fixed-angle rotation, so that the assembly surfaces or the detection surfaces on the workpieces face a working area, the operation of an equipment machine tables is facilitated, the working efficiency is improved, and the labor intensity of workers is reduced. According to the rotary positioning mechanism, conveying lines of the oil pump assembly line are arranged on one sides of the equipment machine tables or penetrate through the equipment machine tables, therotary positioning mechanism is used for loading the workpieces and sequentially conveying the workpieces to all equipment machines along with the conveying lines, the rotary positioning mechanism isjacked out of the conveying lines through a jacking mechanism, and the workpieces are rotated by a certain angle until the assembling surfaces or the detecting surfaces face towards the working area,so that the automatic assembling or detecting engine oil pump can be automatically assembled or detected, the assembling or detecting operation can be carried out on the working surfaces of differentangles of the engine oil pump, the assembly line integration rate is high, and the production efficiency is improved.