This study designed the processing parameters of the flat-plate collector based on the orthogonal arrays. Processing parameters of a flat-plate collector are the key factors affecting its performance. These parameters include the collector tube material, endothermic plate material, number of collector tubes, collector tube diameter, absorption film type, and thickness of the bottom heat insulating material. The quality characteristics include the efficiency coefficient and heat dissipation factor. After the data on each quality characteristic are obtained from the orthogonal arrays, main effect analysis and ANOVA (analysis of variance) are conducted to determine the parameters that have significant effects on these quality characteristics. The data are then preprocessed by grey relational generation, and the optimal combination of processing parameter levels is determined through grey relational analysis and entropy measurement. Three confirmatory tests are conducted, and results indicate that the average values of the efficiency coefficient and heat dissipation factor fall within the 95% CI (confidence interval), the experiment is proven to be reliable and repeatable. According to the response graph of the GRG (grey relational grade), absorption film type is a significant factor that affects the quality characteristics: in other words, the overall quality can be effectively controlled by controlling the only parameter. (C) 2011 Elsevier Ltd. All rights reserved.