Uniaxial compressing creep tests and triaxial compressing creep tests are made on the rock samples taken from the site of Muzhailing tunnel, and the creep properties of the carbonaceous slate are analyzed and described, so as to study the rheologic and mechanic properties of the carbonaceous slate. Conclusion is drawn that the instantaneous strain takes 80% to 90% of the total and that most part of the rheology under high confining pressure is uniform rheology. The major parameters of the carbonaceous slate, such as the elastic modulus, viscous modulus and viscidity coefficient, are obtained by means of fitting analysis on the test data using Burgers rheologic constitutive model.