Abstract: In order to calculate the caving height of rectangular roadway in bedded rock, we considered and studied the differences in physical and mechanical properties of every layer in roadway roof and studied inner force of every layer. We built calculation model of rock beam and calculated force on the ends of the rock beam with structure mechanics. Then, we got the inner force of rock beam with elastic mechanics. Considering the influence of concentrated force on two clamped support ends of beam, we have calculated out the failure point on beam with elastic mechanics. And then we got the height of caving arch and the angle between failure plane and vertical direction. Compared with the result of in-situ test results, the formula we got matches well with real situation.