The invention discloses a spraying self-propelled multi-branch slim-hole completing tool. The tool comprises a spraying short joint connected with the lower end of a completing pipe string, a liner pipe in sealed connection with the spraying short joint is arranged inside the spraying short joint, an annular space with upper and lower sealed portions is formed between the liner pipe and the spraying short joint, a pressure transfer hole communicated with the annular space is formed in the liner pipe, a plurality of branch slim pipelines evenly distributed in the peripheral direction are arranged inside the annular space, inlets of the branch slim pipelines are formed inside the annular space, the outlets of the branch slim pipelines penetrate through the side wall of the spraying short joint, the branch slim pipelines are connected with the side wall of the spraying short joint through a pipeline sealing joint, and self-propelled nozzles are connected to the outlets of the branch slimpipelines. The invention further discloses an operation method of the spraying self-propelled multi-branch slim-hole completing tool. The tool has the advantages that the processing radius is large, the slim hole depth is controllable, and field operation is easy and reliable.