【Objective】 Ecological factors have very important effects on apple qualities. So it is very important to find out the ecological factors limiting the quality of apple in apple production. 【Method】Taking Wangdonggou Watershed in Loess Gully Region as a case, the ecological factors of apple were evaluated by using principal component analysis and fuzzy comprehensive evaluation. 【Result】 In the study area, the ecological suitability was at the level of basically well, with the integrated ecological indices (IEI) being 0.74. It was also quantified that the Loess Gully Region is a good region for growing apple in China. Soil total nitrogen TN, organic matter (OM) and annual precipitation were the ecological factors limiting the quality of apple in Loess Gully Region, and their membership degrees were 0.34, 0.35, and 0.62, respectively. However, the annual mean temperature, the ≥10℃accumulated temperature, the mean temperature in mid-January, the daily range of temperature in summer, the available P and the available K all reached the extremely well level. 【Conclusion】According to the above results, a new way was raised for improvement of the quality of apple.