A parameterized design method for secondary nozzle of hypersonic low temperature(HYLTE) nozzle of DF chemical laser was established in order to provide an available approach to optimize HYLTE nozzle. Four basic geometric parameters and two adjusting parameters were selected for the parameterized nozzle design by analyzing the restriction and sensitivity of those parameters which affect the nozzle performance or configuration. The relative unmixedness was introduced to evaluate the mixing performance of the designed nozzle. Furthermore, a 3 dimensional simulation code was built to compute the flowfield of the nozzle and cavity. It is indicated that the primary performance for nozzle evaluating is sensitive to the basic geometric parameters.