In order to overcome the disadvantages of the existing automatic optical inspection（AOI） algorithm for solder joints,a new inspection algorithm based on weighted bidirectional 2D linear discrimination analysis is proposed,which takes into account the characteristics of AOI and improves the conventional bidirectional 2D linear discrimination analysis by weighting different classes and samples during the calculation of covariance matrix.By this algorithm,more discriminative features can be extracted.The improved algorithm is then applied to the solder joint inspection to automatically classify the solders from different batches.Experimental results show that,as compared with the commonly-used algorithm based on image comparison or image analysis,the proposed algorithm significantly reduces the misdiagnosis rate with the detection speed meeting the practical demands well.