Usually,the surrounding rock of roadway in coal mines is complex and volatile,its mechanical property parameters is not determined easily and quickly,so,the equilibrium arch theory of М·М·Протодьяконовoften result in the errors in the height of caving arch and the pressure value of surround- ing rock of roadway,this influences the accuracy of parameters. The problem can be solved if the height of caving arch is determined by in - situ measurement. In the paper,taking the roadway of a coal mine in Shanxi province as example,a method to in - situ measure the roof subsidence of roadway with roof sub- sidence meter and determine the height of caving arch is introduced,this method is of practical significance and value in engineering for the rational design of support parameters of roadway surrounding rock.