The invention belongs to the technical field of oil production of oil fields, and particularly relates to a high-water-content horizontal well tracer injection water exploration process and a string. The process includes: determining tracers according to fluid properties of a tested well, and screening out the tracers different in characteristics and mutually incompatible according to the number of test segments of the tested well; respectively calculating consumptions of different tracers injected into the formation; sequentially injecting the different tracers into all the intervals through a dual-seal single-clamp string, pulling out the injection string after all the intervals are injected; lowering down a production string, lifting formation fluid to the ground, sampling and testing on the ground, detecting the content and concentration of the different tracers in output liquid, and judging a water production interval according to the detected structure.