The present invention relates to a process of separating and purifying thorium by solvent extraction, comprising: 1) mixing a thorium enrichment with an inorganic acid to produce a feed; 2) mixing a neutral phosphorus extractant with an organic solvent to obtain an organic phase; 3) extracting from the feed with the organic phase to obtain a loaded organic phase; 4) scrubbing the loaded organic phase with a scrubbing solution and then back-extracting thorium with a stripping solution to obtain a thorium solution; 5) mixing the thorium solution with an oxalate to obtain a precipitate, which is then sintered to obtain thorium oxide. The present process allows to increase the purity of thorium from 80%-99% to 99.99% or more with a yield of more than 98%.