The issue of elevated temperatures in power cable areas of long-distance highway tunnels remains pronounced during summer, even under mechanical ventilation. The authors investigate the Shanghai G40 long-distance cross-river tunnel to evaluate the effects of cable heat generation rate, outdoor ambient temperature, and ventilation rate on the temperature distribution within the cable area using computational fluid dynamics simulation. A temperature prediction correlation applicable to tunnel structures is proposed to address key engineering challenges, including defining the extent of high-temperature zones and determining the critical conditions for downstream temperature exceeding regulatory limits. The findings are as follows: (1) Under summer ventilation conditions, the air temperature in the power cable area increases rapidly along the tunnel′s longitudinal direction, indicating a prominent airflowdriven thermal migration effect. (2) The inlet-outlet temperature difference in the tunnel exhibits nonlinear growth with increasing cable heat generation. During prolonged high-load cable operation, the outlet temperature exceeds the safety threshold of 40 ℃. (3) Lowering the inlet air temperature reduces the outlet temperature but enlarges the inlet-outlet temperature difference beyond the allowable limit of 10 ℃. (4) Increasing the ventilation rate by 87.81 m³/s (equivalent to two air changes per hour) decreases the outlet temperature by approximately 3.57 ℃; however, excessively high ventilation rates substantially increase fan power consumption. Therefore, further research is required to optimize ventilation strategies that balance thermal control and energy efficiency.