In froth flotation monitoring, machine-vision-based soft sensors provide stable and reliable online estimations for the concentrate grade, which is difficult to be measured online owing to technical or economic limitations. It is known that the froth surface appearance and movement characteristics of the froth layer are closely related to the froth grade and usually used as visual indicators for the concentrate grade. However, it is hard for the most used handcrafted features to fully explore patterns of froth surface behaviors from appearance and movement perspectives. Furthermore, the relevance between image features extracted from different time intervals and the concentrate grade can be different. To estimate the concentrate grade appropriately, soft sensors need to explore and exploit the different importance in image features extracted at different intervals. In the context of these issues, this study developed a deep learning-based two-stream feature extraction model to extract the froth appearance and movement features. Also, a hybrid prediction model, which contains a time-series analysis module and an attention mechanism, is proposed to build the prediction relationship between image features and the concentrate grade. Comparison experiments using historical industry data verified the advantage of the proposed monitoring method. In addition, industrial experiments conducted in a real-world flotation plant show that the coefficient of determination achieved by this method is 0.9256, which has a 7.9% improvement compared to an existing expert system.