The invention provides a manual-transmission motor vehicle gear automatic detection method and device. The method comprises the following steps: carrying out calibration on a maximum distribution range of relative spatial attitude of each motor vehicle gear, and carrying out gear detection: to begin with, collecting spatial attitude of a motor vehicle, and then, collecting spatial attitude of a joy stick; carrying out conditional sliding window filtering processing, and then, carrying out subtraction to obtain initial space attitude data of the gear at the moment; comparing the initial space attitude data with the maximum distribution range of the relative spatial attitude of the joy stick in each gear calibrated in the step 1) to obtain a detection value of a gear state; carrying out evaluation to obtain an evaluation value of the gear state; and displaying the gear state evaluation value and meanwhile, sending the gear state evaluation value to an upper computer to finish one gear state detection. The method and device carry out rejecting and filtering processing on possibly-occurred interference and noise through an algorithm, thereby improving gear detection result reliability;and during detection, free stroke of the joy stick is taken into consideration, and the gear detection value is subjected to secondary evaluation, thereby improving gear detection accuracy, and enabling gear detection not to be influenced by old and new wear of the motor vehicle.