In order to clarify the degradation characteristics of soil fertility in gravel-mulched field under the condition of continuous cultivation of watermelon in Ningxia. In the main producing area of selenium-sand watermelon of Zhongwei City in Ningxia, 0-20 cm soil samples of the original wasteland, 1-5, 5-10, 10-20 and >20 years of gravel-mulched fields were sampled, and their basic physicochemical properties and key enzyme activities were analyzed and compared. The results showed that: 1)With the increase of cultivation years, soil structure was further deteriorated by soil compaction, and soil water holding capacity was decreased continuously, and soil salinity was in a linear accumulation (R²=0.880 8), and soil organic matter and nutrient contents were in the process of depletion. 2)With the cultivation years increased, the activities of soil urease, alkaline phosphatase and sucrase were significantly decreased, but no significant difference occurred in soil catalase activity. 3)A negative correlation was found between soil enzyme activities and total potassium content. Soil pH and total salt were the main influencing factors on physicochemical properties and enzyme activities in gravel-mulched fields. Therefore, the continuous cultivation of gravel-mulched fields can lead to the decrease of soil key enzyme activities and the obvious degradation of soil fertility.