A modified phase-field model coupling viscoplastic constitutive equations has been built up to simulate the creep process of nickel-base single-crystal superalloys at 1223 K/300 MPa. The kinematic and isotropic hardening effects as well as interactions of slip systems are included in the present model. Under the external tension along [001] direction, the plastic strain prefers to concentrate in the channel vertical to [001] direction, promoting gamma' precipitate to raft along the direction vertical to [001] direction. The interactions between slip systems alter the value of plastic strain and thus the stress field in inner gamma channel. In turn, the stress field readjusts the plastic deformation. The simulative results and experimental data are in good agreement in the initial creep stage. In addition, this modified model gives a possibility to simulate the microstructure evolution during cycle fatigue.