The invention discloses a vehicle-mounted child leaving reminding device and a vehicle-mounted child leaving detection method. The device comprises a voice sensor, a touch sensor, a main control module, a voice alarm, a communication module and a data storage module, wherein the voice sensor and the touch sensor are connected with the signal input end of the main control module; the voice alarm and the communication module are connected with the signal output end of the main control module; the data storage module is connected with the main control module; after an automobile is power off andan automobile door is closed through detection, the voice sensor and the touch sensor are started and respectively perform detection in voice and touch modes; when at least one detection result indicates that a child is left in the automobile, the automobile sends alarm voice and sends information to a specified mobile phone; and an initial state is returned when the automobile door is opened through detection. By the vehicle-mounted child leaving reminding device and the vehicle-mounted child leaving detection method, people around the automobile and specific related personnel can be effectively reminded when the child is left in the automobile.