The stress redistribution phenomenon would be induced after tunnel excavation in a horizontal layered hard and brittle rock mass with high ground stress, which would induce an increase in shear stress, thus resulting in an increase in local elastic strain energy and even rockburst phenomenon. To study the rockburst mechanism of horizontal rock formations under high ground stress, finite difference software is used and two working conditions of horizontal rock formation and complete rock formation are established based on the Daxiagu ultralarge deep tunnel. The rockburst risk of horizontal rock mass is analyzed from the aspects of elastic strain energy and stress path. The research results show that: (1) Under the action of the tectonic stress field, the difference between horizontal rock formation and complete rock formation is large. After tunnel excavation, the strain energy of the annular area where the face of the horizontal rock formation is located is the largest due to excavation unloading, and sudden changes of strain energy occur at different locations around the tunnel before and after excavation. The sudden change of strain energy is smaller after excavation of the complete surrounding rock. (2) The change trends of the maximum principal stress and elastic strain energy under the two working conditions in the stress path are the same. The stress difference between the arch crown and the arch bottom area in the horizontal rock layer increases after excavation, whereas in other areas, sudden changes occur when excavating to the section where the monitoring points are located, which would cause rock deterioration and an increase in the risk of rockburst in the annular area of the face.