The based membrane extraction of Th(IV) and Yb(III) was studied with HBTMPP in heptane. The separation process of Th(IV) and Yb(HI) was proposed to be a kinetics competition one. The separation of mixture Th(IV) and Yb(III) was carried out by two successive extraction and stripping simultaneously. The concentration ratio of Th(IV) and Yb(III) is 16.74 in the stripping solution. The recovery of Th(IV) is 71.6%. The purity of Th(IV) is 95.74%. The separation factor of Th(IV) and yb(III)is 2.52× 106, which was obtained by interfacial kinetics.