Industrial two-dimensional (2D) matrix symbols are ubiquitous throughout the automatic assembly lines. Most industrial 2D symbols are corrupted by various inevitable artifacts. State-of-the-art decoding algorithms are not able to directly handle low-quality symbols irrespective of problematic artifacts. Degraded symbols require appropriate preprocessing methods, such as morphology filtering, median filtering, or sharpening filtering, according to specific distortion type. In this paper, we first establish a database including 3000 industrial 2D symbols which are degraded by 6 types of distortions. Second, we utilize a shallow convolutional neural network (CNN) to identify the distortion type and estimate the quality grade for 2D symbols. Finally, we recommend an appropriate preprocessing method for low-quality symbol according to its distortion type and quality grade. Experimental results indicate that the proposed method outperforms state-of-the-art methods in terms of PLCC, SRCC and RMSE. It also promotes decoding efficiency at the cost of low extra time spent.