The invention discloses a solid oxidizing agent fixed-depth adding monitor for underground water, and belongs to the field of underground water monitoring. A monitor has an underground part and an overground part, which are respectively connected with a measuring tape. The underground part is a steel container, and comprises a steel inner tube (1), a steel outer tube (2), a steel fixed pedestal (3), a detachable protection probe steel pipe (4), an underground water monitoring probe (5), a measuring tape (6), a steel wire rope or a nylon rope, a circular ring, a steel mechanical arm (9), and amovable steel plate (10). The overground part is a shaft-type measuring tape. The monitor simplifies the operations of the detection of the indexes of redox potential, pH value, dissolved oxygen and conductivity of underground water during the adding of a solid oxidizing agent, can determine whether to add the solid oxidizing agent or not according to the above indexes, achieves the adding of thesolid oxidizing agent to an underground water well at a certain depth, reduces the loss of the solid oxidizing agent when the solid oxidizing agent initially makes contact with the water surface, andimproves the precision of the adding depth of the oxidizing agent, the synchronization of underground water data, time cost and manual efficiency.