The invention provides a safety door opening early warning device used after an automobile is parked, and belongs to the technical field of automobile safety. The safety door opening early warning device used after the automobile is parked comprises an automobile door lock system, a radar sensor, a pressure sensor, an information processing module, a digital signal processing system, an alarm system and an interface data processor. The information processing module comprises a filter, a high-frequency amplifier and an A/D converter. After the automobile stops, an automobile electronic control unit transmits the signal that the speed V is equal to 0 to the digital signal processing (DSP) system through the interface data processor, then a command is sent to the radar sensor, the radar sensor starts to emit 24 GHZ high-frequency short waves outwards, wave return signals are received through a receiving antenna, the wave return signals are analyzed and processed through the DSP after smoothing, amplifying and A/D converting are conducted, and then the monitored situation is fed back to a driver timely, so that the driver can open the car door safely. The safety door opening early warning device is simple in hardware structure, and the radar sensor is stable in work, lower in cost and convenient to popularize.