The invention provides a vehicle-mounted holographic display device. The vehicle-mounted holographic display device comprises a holographic display module, a road condition acquisition module and a control module, wherein the holographic display module is used for forming a viewing visual area for watching holographic representation images in the rear of a vehicle; the road condition acquisition module is used for acquiring a road condition level of the road where the vehicle is located; the control module is connected with the holographic display module and the road condition acquisition module and used for sending a corresponding control signal to the holographic display module according to the road condition level, and the corresponding viewing visual area is formed by the aid of the holographic display module according to the control signal. Correspondingly, the invention further provides a vehicle-mounted holographic display method. With the adoption of the vehicle-mounted holographic display device and the vehicle-mounted holographic display method, a safe distance with the rear vehicle can be kept, and traffic accidents are reduced.