The invention provides a technology for extraction and separation of thorium and rare earth, wherein the technology comprises the steps: firstly, dissolving prior dissolved slag produced in a monazite treatment alkaline-process technology by using hydrochloric acid to obtain a material liquid containing thorium, rare earth and uranium; taking P350 as an extractant, extracting and separating thorium and rare earth in the material liquid containing thorium and rare earth in a high-acidity hydrochloric acid system, to obtain a thorium-loaded organic phase and a raffinate; washing the thorium-loaded organic phase with high-acidity HCl, then carrying out back extraction by using a solution containing HNO3 and NaNO3 to obtain Th(NO3)4 back-extracted solution; and allowing the raffinate containing rare earth and high-concentration hydrochloric acid and obtained from extraction and separation to return to a prior dissolving process. The separation coefficient of thorium and rare earth can be effectively improved in the high-acidity extraction system, the separation efficiency is improved, the separation effect of rare earth and thorium is improved, high-purity thorium nitrate is obtained, rare earth and other valuable elements in the raffinate are comprehensively recycled, the hydrochloric acid in the raffinate is comprehensively utilized, the utilization rate of resources is improved, the postprocessing process is reduced, environment pollution is reduced, and the comprehensive utilization of the resources is achieved.