Abstract: Plastic analysis of the circular roadway surrounding rock with the lateral pressure coefficient of 1，is made based on the Drucker-Prager criterion，obtaining the analytical solutions of plastic zone's radius.The cases are analyzed based on the specific geological conditions and the numerical simulation on the stress field and displacement field of the surrounding rock is made.The results show that stress field and displacement field are all distributed symmetrically.The surrounding rock around tunnel emerges stress concentration and reduction.Thus，roadway should be supported timely after being excavated，and the supported strength of the roadway shoulder and the bottom corner be enhanced.The value of vertical displacement is greater than that of horizontal displacement，and the displacement is reducing gradually till to be 0 with the surrounding rock extending to the depth.

Key words: Drucker-Prager criterion, Stress field, Plastic zone