When dyeing of cotton fiber with reactive dyes, the lower utilization of reactive dye, high salt dosages and residual dyes have caused serious environmental problem and resources wasting. In this paper, Ge-lin-lan modifier was chosen to modify pure cotton fabric to dye in salt-free dyeing bath, which optimizing the best process of modification. The results showed that the optimum parameters of modification by two-bath exhaustion process are: the dosage of Ge-lin-lan modifier is 4% o.w.f., pH is 9-10, liquor ratio is 20:1, temperature is 80℃, and time is 30min. The result of one-bath exhaustion process is not as good as that of two-bath exhaustion process. It can't meet the need of production. Investigating the dye performances of modified cotton fabric and the control sample with reactive red X-3B, it indicated that the former possess higher K / S value, dyeing rate, leveling properties and exhaustion percentage. The dyeability of modified cotton fabric is good compared with the unmodified cotton fabric. Salt-free dyeing on cotton fabric with reactive dyes can be achieved.