The invention discloses a method and a device for prompting a vehicle energy efficiency state for a driver in real time. The device comprises a microprocessor, a storage, a graphic display, a digital communication interface connected with a vehicle power device electric control unit, and the like. The device pre-stores an energy efficiency characteristic curve graph in the storage and displays the energy efficiency characteristic curve graph on the graphic display, is connected with the electric control unit of the power device through a data bus link to form a communication network, reads and records the rotating speed and torque of the power device and dynamically displays the rotating speed and torque on the display. The device can be arranged in an automotive instrument desk or an automotive central control desk, can make the driver intuitively observe the position of the current working characteristic point of the vehicle power device on the energy efficiency graph and the offset of the position with an optimal working area target position, prompts the driver to timely perform reasonable gear adjustment and other operation according to specific road conditions, cultivates good driving habits, improves the driving level and improves the fuel economy of the vehicle.