One kind of vehicles back-draft path auxiliary unit, provides the driver in the vehicles back-draft when knew in advance that vehicles' back-draft path, it is mainly carries on because of a phantom technology signal of application and the steering wheel corner by way of the path information bank or mathematics equation the operation, and will operate the result to paste picture in the image output display unit, and using supersonic wave distance-measuring radar obtained with obstacle distance, supplies adjustment of reference the internal image process, so as to provides one can the immediate rapid reaction, the serviceability with install the simple vehicles back-draft path auxiliary unit high, reduces the manufacturer and characteristic of effectively the consumer cost burden.