The present invention relates to an automatic detection method and apparatus, and particularly is a fast evaluation method and apparatus applied to seed cotton impurities in a seed cotton purchasing link. In an existing seed cotton purchasing process, a seed cotton impurity analytical engine is mainly used for performing an impurity separating test on seed cotton to detect a percentage of impurities, in which an impurity detection procedure is complicated and is slow in speed. As a result, a phenomenon of seed cotton transport vehicle queuing is serious. The fast evaluation method and apparatus proposed in the present invention are used for resolving a problem that a speed of detecting a percentage of impurities in seed cotton is slow in a purchasing process. The fast evaluation apparatusin the present invention comprises a pneumatic cotton delivery apparatus, a seed cotton large-impurity cleaning apparatus, a pushing apparatus, a seal capping apparatus, a conveying apparatus and an online imaging detection apparatus. The evaluation method and apparatus resolve technical problems that a procedure of detecting a percentage of impurities in seed cotton in a purchasing process is complicated and slow in speed and the like, and provides a real-time basis for seed cotton transaction settlement.