By measuring the creep curves at medium temperature and high stress of a nickel-base single crystal superalloy and analyzing the microstructure and dislocation configuration diffraction after creep fracture, the microstructure evolution and deformation mechanism of the single crystal alloy were researched. The results show that the alloy creep activation energy Q is (462 ± 20) kJ/mol under the medium temperature and high stress conditions, and the apparent stress exponent na is 4.34, indicating that the alloy possesses better creep resistance in the measuring temperature and stress range. Dislocation diffraction contrast analysis indicates that the super dislocations <110> that cut into g￠ phase both slip in the {100} cube slip systems and in the {111} octahedral slip systems during creep. The dislocations of movement meet and a dislocation reaction can occur to form a super dislocation which can cross slip to the cube {100} slip plane. A reaction can occur for the motion dislocation which meet in two different six-sided {100} slip planes, and the resulting dislocation can move in the {111} octahedral slip systems