The differences of laying way and soil environment along the way result in the current-carrying bottleneck of cable line, which determines the load capacity of the total cable line. A method for identifying the bottleneck of cable line is proposed based on the evaluation of cable conductor temperature. In view of the actual situation of 220 kV Qilin-Tianhe Line I & II of Guangzhou, the current-carrying capacity bottleneck is identified in typical scenes, and the time-space characteristics of current-carrying capacity bottleneck are analyzed, the load capicity of the line is evaluated. The results show that the capacity bottleneck of line is related to the magnitude of load and season at continuous load, and the capacity bottleneck of line is related to the magnitude of initial load current, the length of the emergency time, the magnitude of emergency current at emergency load. The research results can provide technical support for load dispatching of complicatedly laid transmission cable line, and improve the safety of cable operation at peak load.