The invention relates to the technical field of injectors, in particular to a dosage-adjustable injector based on a rotary suction type. The needle tube is installed at the inner end of the needle sleeve, the push tube is installed at the inner end of the needle tube, baffles are arranged on the two sides of the tail end of the needle sleeve, scale rods are arranged on the side faces of the baffles, dispatching blocks are connected to the scale rods in a threaded mode, the push tube is matched with the inner end of the needle tube in a telescopic mode, sleeves are arranged on the two sides of the push tube, and the sleeves are matched with the scale rods in an inserted mode. Through the scale rods and the dispatching block, in the injection process, the dispatching block is rotated to move to the required metering scale position, the pushing tube is pushed at the moment, medicine at the inner end of the needle tube is pushed out through the pushing head, the two sleeves and the two scale rods slide at the moment, and when the tail ends of the sleeves make contact with the dispatching block, the pushing tube cannot continue to slide; at the moment, required metering is completely injected into an injector, metering of injected medicine can be adjusted, injection efficiency is improved, and the situation that patient recovery is affected by inaccurate metering caused by manual injection is avoided.