Based on the sensitivity analysis at annual, monthly and daily scales, parameters of the Xinanjiang model could be divided into three groups and optimized independly without considering the effects from other groups. This paper focuses on the optimization of data adjustment parameters, Cp and Cep, which are sensitive at annual scale. The concept of aridity index is introduced into the optimization process, and proposed a relationship describing Cp and Cep as a function of annual runoff coefficient and pan aridity index. Three different methods are developed to estimate the value of Cp and Cep in ideal condition and actual practice respectively. The results show that, compared with optimizing Cp and Cep independly, the method considering the relationship of runoff coefficient and pan aridity index will narrow the parameter space, and keep the same accuracy. The effectivity of method using the simple linear relationship will depend on the length of data series and correlation between annual runoff coefficient and pan aridity index.