The invention relates to a method and device utilizing a solid point source to calibrate a liquid effluent monitor. The device comprises a fastening ring and three scales, wherein the first scale is fixed on the fastening ring, the second scale is perpendicularly connected with the first scale, a coordinate of the second scale on the first scale can be adjusted through adjusting thread of the first scale, the third scale is perpendicularly connected with the second scale through a sliding rule and can move relative to the second scale, a tail end of the third scale can be equipped with the solid point source, the fastening ring is fixed at one end of a pipeline identical to materials and internal and external diameters of a pipeline measured by the monitor, and the fastening ring and the pipeline are concentrically arranged. Through a value integration means, detection efficiency of the monitor for certain-energy gamma rays of a liquid source can be lastly acquired. The method is advantaged in that inconvenience caused by liquid source calibration can be avoided, and measurement of the solid gamma point source is only needed in the whole process.