To meet the environmental and scenic demands,some rocky slopes in civil engineering need some works on ecosystem restoration.Firstly,the present methods in rocky slope ecological protection engineering are summarized Then,the changes of gunning (or gunniting) soil layer in rocky slope ecological protection engineering projects are investigated. By using the principle of mass balance and the mult-i subject know -ledge, an inequality for the mass balance of the gunning soil layer on rocky slope is set up, all the factors in the inequality are analyzed, and the figures on the changes of gunning soil layer on rocky slope under different situations are presented. It is found that water erosion,landslip loss,and initial thickness of gunning soil layer are the key factors of soil conservation. Based on the above fact, some measures on how to guarantee the success in rocky slo pe ecological protection engineering projects are discussed. This paper may help the practice of rocky slope ecological protectio n engineering projects in the future.