To establish a protection method for the surface of a water shutoff sheet which admits easy execution of construction works and also maintenance and management and can effectively prevent deterioration or damage of the sheet caused by an external action by covering the sheet portion on a slope in stabilized condition.

This method is to protect the surface of a water shutoff sheet 11 to be laid on a slope 13. A mesh mat 14 in the form of dishcloth gourd structure formed from a number of wires in entanglement assuming a number of irregularly shaped loops is laid on the surface of the sheet 1 in such a way that the top in the fixed condition is spreading toward the bottom of the slope, and a base material for greening is sprayed to this mesh mat 14 and deposited on the sheet surface and retained with the mat 14 interposed.