The invention provides a compound low-density cement early-strength agent as well as a preparation method and application thereof. The compound low-density cement early-strength agent consists of the following substances in percentage by weight: 70-90 percent of silicate, 10-30 percent of aluminate and 0.5-1 percent of triethanolamine. The compound low-density cement early-strength agent is good in compatibility, can accelerate hardening and condensation of low-density cement slurry, shorten the cementing and curing waiting time and effectively improve the low-density cement early strength. The compound low-density cement stone early-strength agent does not contain chloride ions and other corrosive ions, and has no corrosive effect on sleeves and cement tones. Adopted raw materials are more universal; the preparation method and required equipment are simple in conditions and are easy to implement. The compound low-density cement early-strength agent provided by the invention not only can meet performance requirements for the low-density cement slurry and the cement stones in the cementing construction, but also can effectively protect the sleeves, protect oil and gas reservoirs and improve the single well productivity. While economic benefits are obtained, the compound low-density cement early-strength agent also has obvious social benefits, thereby being worthy of popularization and application.