The invention discloses a variable-throat-diameter safety valve, which comprises a case, a main spring mechanism, an auxiliary spring mechanism, a connector, a main valve disc and an auxiliary valve disc, wherein the lower end of the case is connected onto a valve nozzle in a sleeving manner, the main spring mechanism, the auxiliary spring mechanism, the connector, the main valve disc and the auxiliary valve disc are arranged inside the case, in addition, the upper half part of the connector is a sealed part, the lower half part of the connector is an open part, the top of the connector is fixedly connected with the main spring mechanism, the bottom of the connector is fixedly connected with the main valve disc, and the bottom of the auxiliary spring mechanism is fixedly connected with the auxiliary valve disc. The variable-throat-diameter safety valve provided by the embodiment of the invention has the advantages that one set of the auxiliary spring mechanism and the auxiliary valve disc is additionally arranged in the safety valve, and in addition, the jumping pressure of the main valve disc mechanism and the jumping pressure of the auxiliary valve disc mechanism are set to a state that one pressure is high and the other pressure is low, so two discharging passages with different rated flow rates are formed, the safety of the safety valve is ensured, and the problems of vibration and frequent jumping of the valve discs are avoided.