The trenching construction is an important process for underground diaphragm wall, YCJF20 percussive and reverse circulation rig is used in trenching construction of underground diaphragm wall in a station of Xiamen metro line 3. This paper introduces YCJF20 rig about its main technical parameters, characteristics and working principles, as well as the construction process of guide wall and guide hole, drilling rig layout, mud preparation and trenching by percussive drilling.