The invention discloses an automatic car-following method and device, and belongs to the field of vehicle active safety. The automatic car-following method includes the steps that n strengthening signal values are obtained by equally dividing the car-following distance into n sections and determining strengthening signal values for sub-areas corresponding to all the sections of the distance, the car-following distance is a preset driving distance of a local car following a front car, the area corresponding to the car-following distance is a reliable area, and n is an integer larger than 2; n normalization values are obtained by carrying out normalization on the n strengthening signal values; whether the local car is in the reliable area or not is judged according to the n strengthening signal values, the n normalization values and the current driving position of the local car; when the local car is in the reliable area, the local car is controlled to finish the automatic car-following motion through a machine study method. The automatic car-following method resolves the problem of low reliability of automatic car-following, realizes the effect of improving the reliability of automatic car-following, and is used for automatic car-following.