This study develops a fractional wind-solar-nuclear-oriented low-carbon electric power system planning (FWLE) model. The FWLE model can provides the optimal policies relating to electricity generation structures, carbon/pollutant emission mitigations, and system benefits under the objective of minimizing carbon intensity (CRI). The interactive effects between wind, nuclear, and solar electricity generation ability on the system performance are also identified through scenario analysis. The model is applied to Fujian Province (in China) to verify its feasibility. Under the designed 27 scenarios, the CRI would fluctuate between 2.97 and 4.22 kg/RMB¥. It is implied that the generation ability has obvious effect on making sustainable system planning policies. The main effects are ranked as: photovoltaic power > wind power > nuclear power. under all scenarios, the total capacity expansion would first increase (before 2034) and then decrease. Under the most risk reverse scenario (S1), the capacity would slowly increase to 1868.68 MW in 2034 and decrease to 413.29 MW in 2060; under the most risk acceptance scenario (S1), the capacity would quickly increase to 2578.91 MW in 2034 and decrease to 584.35 MW in 2060. Over the planning horizon, coal-fire power, nuclear power, wind power, and photovoltaic power would averagely contribute about 27.04%, 32.59%, and 17.68%, and 8.89% to the total electricity generation, respectively. Decision makers can select proper plans according to their preferences.