An agravity-type solid and liquid feeder features that the weighing unit for feeding liquid has metering and external metering drums connected respectively to load sensors, and the single (or dual) screw feeding mechanism for feeding solid has a dished hopper under feeding hopper. Its metering-mixing method includes such steps as setting up the mixing rate by industrial control computer, obtaining weigh signal by load sensor, transmitting it to PLC module, and outputting real-time regulating signal to feeding unit for controlling the feeding while regulating the flow stability.