The invention discloses a monitoring device based on a ship diesel engine. The monitoring device comprises a processor, a power supply, a first temperature sensor, a second temperature sensor, a pressure sensor, a speed sensor, a speed signal conditioning module, a key module, a display module, an alarm system, a relay control circuit and an RS485 communication module. According to the monitoringdevice, the real-time water temperature, oil temperature, oil pressure and speed information are obtained through the arranged multiple sensors, then through the processor combined with related rules,the corresponding water temperature, oil temperature, oil pressure and speed information are acquired at set intervals, whether operation is abnormal or not is known by combining related algorithms,when operation is abnormal, automatic alarming and displaying through the display module are achieved and alert working staff; and then whether the engine is in a danger state or not is known by judging the real-time water temperature, oil temperature, oil pressure and speed information, meanwhile, the danger level is obtained, operation of the diesel engine is timely stopped when the danger stateemerges, and an alarm is given out.