Joints are crucial factors in rock masses engineering,so using stress waves to invert joint attitude is a valuable practice.The stress wave emitted from a vibration source is reflected by joints and returns to the ground.A formula to calculate the reflected wave travel time was deduced using analytic geometry theory.In the formula,a direct relationship was established between a joint's real dip angle,real dip direction and the travel time at test spots on the ground.The reflected wave's isotravel time circle described by the formula has a clear conception and a definite meaning.Using the program on the MATLAB platform,this formula can be applied to invert the joint attitude by searching the center of the circle based on the measured travel time at the testing spots around the wave source.