By means of tensile and compression creep testing and SEM, TEM observation, an investigation has been made into the microstructure evolution of a single crystal nickel base superalloy during tensile / compression creep. Results show that the cubic γ′ phase in the superalloy is transformed into the N-type meshlike structure along the direction vertical to stress axis during tensile creep. The cubic γ′ phase is transformed into the P-type structure along the direction parallel to stress axis during compression creep. An obvious asymmetry strain of the alloy occurs during tensile and compression creep, the formation of the needle-like γ′ rafts during compression creep is a main reason of the alloy displaying a smaller strain. During compressive creep, the deformation feature of the alloy is the <110> and (1/3) <112> super dislocations shearing into the γ′ rafts. The deformation mechanism of the alloy, in the stage state of tensile creep, is dislocation climb over the γ′ rafts.