The invention provides a turnover mechanism for a hollow injection-blow molding machine. The turnover mechanism comprises a demolding frame; a first rotating shaft and a second rotating shaft are separately installed at the two ends of the demolding frame; the first rotating shaft and the second rotating shaft are separately connected with the two ends of a rotary arm; a demolding plate is installed on the rotary arm; a gear is installed on the first rotating shaft; a gear rack mounting seat is installed at one end of the demolding frame; a cylinder is installed at the lower part of the gear rack mounting seat; a piston is arranged in the cylinder and is provided with an integrated piston rod provided with a gear rack; and the gear rack penetrates into the gear rack mounting seat and is meshed with the gear. According to the turnover mechanism provided by the invention, an oil cylinder is used for providing a driving force; the demolding plate installed on the rotary arm can be turned over rapidly and stably by virtue of a transmission mechanism consisting of the gear rack and the gear; the stress condition during action execution is improved so that the oil cylinder can be miniaturized and simplified, the cost is lowered, the overall mechanism becomes more compact, and convenience is provided for mounting and dismounting of the equipment.