Blind number theory was used to evaluate water environmental carrying capacity (WECC) in mining cities of central Liaoning Province, P. R. China to prompt the balanced development of water environment with human activity. The research was based on the characteristics of water environment systems with numerous uncertainties such as random, fuzzy, and grey ones which may occur simultaneously or partially in a system. An indicator system for WECCs was established. The indicators were set as blind number and the WECC in mining cities of central Liaoning Province subsequently were calculated. Study results show that from 1997 to 2005, the WECCs in the mining cities Anshan and Fushun of central Liaoning Province were below the safe level, but the WECC in Benxi city was rather safe. By the comparative analysis of a system under uncertainty with that under a condition of certainty, the results of the blind number model regarding WECC was reasonable. This model is well adapted for WECC assessment.