Abstract: Correct evaluation of regional water resources carrying capacity has practical significance not only to the efficient and reasonable utilization of the water resources but also to the sustainable development of regional socio-economy. Γ-type distribution curve was adopted to simulate water resources carrying capacity evaluation. A universal Γ-type distribution function for water resources carrying capacity evaluation was proposed based on the selected reference value of all indicators and the appropriate standardization transformation formula. The universal Γ- type distribution function can ignore the influence of index number by means of normalization data processing mode. Particle swarm optimization was used in optimization of the parameters in the formula. The optimized Γ- type distribution function was used in water resources carrying capacity evaluation of the Manas River Valley and the Tarim River Basin. Results of the two cases agreed with that of other evaluation methods, and showed that the formula was not restricted by the number of the evaluation indexes and by the differences of the index system. The evaluation method can save the complex programming calculation work and provided a new approach to the evaluation model which is universal and simplified. In the practical evaluation, even water resources carrying capacity index system of testing sample was different from the index system in the article, the Γ-type distribution function can also evaluate it directly by means of normalization data processing mode.