Abstract: At present, the simple heat injection string pipes used by multiple thermal fluids technology in offshore wells have poor whole-pipe thermal insulation, and are uneven in multiple thermal fluid injection of horizontal sections. In order to solve these problems, high-efficiency injection strings for offshore multiple thermal fluids were designed by developing key thermal insulation tools and step heat injection tools and by designing horizontal sections for heat injection by sections. The thermal insulation section of the string consists of insulated tubing, insulated coupling, insulated centralizer, insulated compensator and insulated packer. Due to its excellent insulation performance on the whole, the heat loss of injected thermal fluids dropped. Its horizontal section, which could implement even heat injection in horizontal sections, consisted of uniform fill-up valves, segmenting packers and tubing centralizers. All key insulated tools and step heat injection tools could meet the requirements for long-term operation at 330 degrees and with Grade D in heat insulation performance. The uniform heat allocation device had been applied 7 times to wells with implementation of uniform heat injection in horizontal sections. In summary, multiple thermal fluids could be injected efficiently offshore by using the high-efficiency multiple thermal fluid injection strings together with the corresponding key tools.