Performance and application of the self-made flame retardant DDTS to flame retardant finish of cotton fabric are studied．The results show that the optimum flame retardant finishing process is DDTS 250g/L ,with the solution pH value of 7, curing not more than150℃ for90-120s．The finished cotton fabric features excellent flame retardancy, is assessed B1 level. Besides, little strength loss and whiteness loss are observed.