Cationic polymers have been used in the cationization of cotton fabrics for salt-free dyeing, but commonly used polymers are limited by their high molecular weight and low adsorption efficiency, leading to high dosage or complex modification conditions. In this study, polyallylamine with low molecular weight was found to be an efficient cationic agent for cotton modification and the modified fabrics can be salt-free dyed with different kinds of reactive dyes after the optimization of the modification process. Furthermore, the modification bath was reused by replenishing a small amount of cationic agent and adjusting the pH to the original level. The results showed that all the salt-free dyed cotton fabrics had excellent performance when the fabrics were modified with a 2 g L