A system for diagnosing breakdowns of a switch by using plural light emitting diodes (LEDs) on a front panel (10) of the switch includes: plural port LEDs (31, 32, 33, 34, . . . 3n), a user interface (50) for generating an instruction to convert display modes of the port LEDs, a CPU (central processing unit) (60) coupled to the user interface for dealing with the instruction, an LED driver (70) coupled to the port LEDs for refreshing the displays of the port LEDs; a physics (PHY) module (80) coupled to the LED driver and used for obtaining the operation statuses of the ports; and a periodic service manager (90) coupled to the LED driver for triggering the LED driver periodically. Display modes of the port LEDs can be converted selectively, which reduces the number of port LEDs needed, and still allows administrators to conveniently diagnose any breakdowns of the switch.