A nest RT-PCR/restriction test has been developed in order to distinguish the lapinised vaccine strain from field isolates of classical swine fever virus. The restriction enzyme cut sites mapping of the major coding sequence of E2 gene lapinised vaccine strain and ShiMen strain of classical swine fever virus have been compared. Ten and sixteen unique restriction markers have been found in the lapinised vaccine strain and ShiMen strain. The restriction enzyme cut sites mapping of the twenty six unique restriction marker in the major coding sequence of E2 gene of 17 classical swine fever field isolates have been analyzed. Only 3 sites (HgaI、Hin8I及Hsp92I) are present in the lapinised vaccine strain sequence. Two pans of nested primers and a criteria of analysis have been designed for HgaI restriction marker site. The tests have been conducted first on the lapinised vaccine strain and ShiMen strain of classical swine fever virus resulting in predicted restrection patterns. Finally, the tests have been applied to 5 field isolates of different gene group analyzed by phylogenetic study. The result showed that only HCLV strain gene can be cut to 2 fragment by Hgal , and ShiMen strain and 5 field isolates cant be cut At the same time the sensitivity and specificity of nest RT-PCR have been tested. The sensitivity is 0. 2MLD. The specific fragment of BDV and BVDV were not obtained by the nest RT-PCR. These results showed that the development of the nest RT-PCR/restriction tests is very important for the control and perish of classical swine fever in china.