Abstract: Citrus tristeza virus（CTV）causes stem pitting and quick decline that have caused devastating losses in global citrus production. At present，the best means to protect commercial citrus against endemic stem pitting isolates of CTV has been cross-protection with appropriate mild CTV isolates. Research was directed towards the selection and screening of mild strains of CTV which could protect against sour orange decline strains. In this paper，progress in cross protection against CTV，the screening of mild strains of CTV and the mechanism of cross protection were reviewed. Furthermore，the possible disadvantages for using cross protection against CTV were also discussed in order to lay a sound foundation for better control of the damage caused by CTV.

Key words: Citrus tristeza virus, cross protection, screening of mild strains, research advance