Abstract: This article researched the analytical method of classical elastic-plastic problems in rock mechanics, based on the limit equilibrium theory, combined with the stress balance principle, proposed a new method of calculating the width of plastic zone in rectangular coal roadway. The engineering examples and numerical simulation is applied to verify this new method. The results show that the calculation results of new method with the results of numerical simulation and engineering actual situation are relatively consistent. The new method is more precise compared with other methods. It can provide more accurate design parameters for coal mine roadway support design. The new method has application value in practical engineering.