The invention discloses a fracturing recovery fluid water treatment agent adding metering device and a method. The device comprises a flowmeter, an industrial personal computer (IPC), a valve and a single-dosage water treatment agent adding system formed through orderly connection of a liquid storage tank, a metering pump and the valve via a connecting pipeline, wherein the single-dosage water treatment agent adding system is connected with a mixer, the metering pump is connected with the flow controller through the IPC; the mixed liquid input end is provided with the flowmeter and connected with the IPC; the singe-dosage water treatment agent is dissolved or diluted by the water and then stored in a single liquid storage tank, the concentration data is recorded in the IPC, the control valve corresponding to the single liquid storage tank is opened, the flowmeter measures the water treatment amount of the recovery fluid, the IPC computes the flow of the single dosage of the water solution according to the concentration and the set adding amount of the single dosage, the flow controller controls the metering pump to add the single-dosage water treatment agent with set proportion so as to obtain the water softener, and the water softener is uniformly mixed with other single-dosage water softeners in the mixer. The device disclosed by the invention has the advantages that the usage amount of the water treatment agent is precise, and the automation degree is high.