The invention discloses a device and a method for detecting and recording abnormity on the basis of a watchdog in a PON (Passive Optical Network) access system. The device comprises a hardware watchdog, a software watchdog, a log recording module and a CLI (Command-Line Interface), wherein the software watchdog comprises a configuration management module, a task state detection module and a CPU (Central Processing Unit) utilization ratio detection module; the task state detection module is connected with the log recording module and used for polling the task sate of the system; the CPU utilization ratio detection module is connected with the hardware watchdog and used for detecting the CPU utilization ratio of the system; the task state detection module is communicated with the CPU utilization ratio detection module through a pipeline communication mode; the software watchdog is used for outputting a reset signal to a hardware watchdog timer at regular time; and when abnormity is detected, a zone bit is set, zero clearing is stopped by the log recording module after the abnormal information is recorded by the log recording module, a master control panel is reset, and changeover is triggered. According to the invention, a master panel is automatically reset to recover a system service when the master control panel is abnormal, and the abnormal data is recorded before resetting, which is beneficial to positioning faults.