The three Gorges reservoir waterdiversion project is a new line of the SouthNorth WaterDiversion Project. The paper studies several major factors which affect the crustal stability in the region. These factors are deepseated structures,tectonic stress fields,fault activity,earthquake activity and rock properties. In order to improve the accuracy and adaptability of evaluating regional crustal stability, with an emphasis on stability of long deep buried tunnels of waterdiversion project on two orders of structural stability and rock mass stability, the authors select dominative conditions which affect regional crust stability as evaluating factors, establish fuzzy evolution model, and fuzzy comprehensive evaluation method. The stability of engineering ground is assessed in terms of structural stability and rock and soil stability using a comprehensive assessment model of fuzzy mathematics. The result shows that the engineering field of the waterdiversion project is of high crustal stability and suitable for building large water diversion projects. Of all the thirty regions, the most unstable region (one) covers an area of 699 km2, accounting for only 1.3% of the total engineering field area (about 52577 km2); relatively stable regions (eight) cover an area of 15826 km2, 30.1% of the total area; stable regions (twenty one) cover an area of 36052 km2, 68.6% of the total area. Three designed water diversion lines were optimized and compared using the crustral stability assessment method, indicating that the middle line is the best.