Abstract: In this research，a novel method to develop co-dominant SNP markers which was called double SNP markers was developed. This new approach was used to obtain a double SNP marker named NL2-3 of Ty-1 gene resistant to TYLCV（Tomato yellow leaf curl virus）in tomato. The process of developing the NL2-3 double SNP marker included two main steps：Design specific primer pairs of resistant and susceptible genes individually based on two ideal SNP sites and mix the two specific primer pairs in one PCR reaction system with a proper ratio. With SNP marker NL2-3，we identified 5 resistant and 7 susceptible inbred lines and 3 homozygous Ty-1/Ty-1 resistant individuals，11 heterozygous Ty-1/ty-1 ones and 2 homozygous ty-1/ty-1 susceptible lines from F3 segregation population. This result was consistent with the field inoculation assay. We concluded that as the first double SNP marker of Ty-1 gene，NL2-3 can be directly applied to marker-assisted selection and would speed up the screening ofresistant breeding and cultivar evaluation.

Key words: tomato, Ty-1, double-SNP marker