The mechanism of microstructure evolution and its effect on the mechanical properties of nickel-based single-crystal superalloys during creep at high temperatures and low stresses are critical to the development of advanced single-crystal superalloys for aeroengines with high thrust: weight ratios. In this work, the microstructural evolution of a fourth-generation nickel-based single-crystal superalloy during creep at 1100^oC for 200 h at various stress levels was investigated using a specially designed sample with variable cross-sections, with the aim of obtaining different applied stresses synchronously on a single sample. The effects of applied stress on γ/γ' microstructure, interfacial dislocation configuration, alloy element partitioning behavior, and lattice misfit of γ/γ' phases of the used single-crystal superalloy were also studied, as were the effects on room temperature Vickers hardness. The results indicated that the typical rafting microstructure was formed during creep over the 200 h period at 1100^oC under various stress levels. With increasing applied stress, the volume fraction and rafted thickness of the γ' phase gradually decreased, while the rafting degree of the γ' phase and the channel width of the γ phase gradually increased. A dense interfacial dislocation network was formed at the γ/γ' interface, and interfacial dislocation spacing decreased with increasing applied stress. Simultaneously, increased partitioning of solution-strengthening elements Re, Mo, and Cr to the γ phase and increased partitioning of γ'-strengthening element Ta to the γ' phase resulted in a larger absolute value of γ/γ' lattice misfit at higher stress. In addition to the decreases in volume fraction and rafted thickness of the γ' phase and the increase in channel width of the γ phase, another important factor in the strength decline of the single-crystal superalloy was the pile-up of dislocations at bent γ/γ' interface boundaries, mainly caused by the dissolution of the γ' phase and promotion of dislocation shear into the γ' phase. This work provides a basis for quickly establishing the relationship between creep conditions and microstructure evolution of nickel-based single-crystal superalloys.