Diabetic retinopathy (DR) and its complication, diabetic macular edema (DME), are major causes of visual impairment and even blindness. The occurrence of DR and DME is pathologically interconnected, and their clinical diagnoses are closely related. Joint learning can help improve the accuracy of diagnosis. This paper proposed a novel adaptive lesion-aware fusion network (ALFNet) to facilitate the joint grading of DR and DME. ALFNet employed DenseNet-121 as the backbone and incorporated an adaptive lesion attention module (ALAM) to capture the distinct lesion characteristics of DR and DME. A deep feature fusion module (DFFM) with a shared-parameter local attention mechanism was designed to learn the correlation between the two diseases. Furthermore, a four-branch composite loss function was introduced to enhance the network’s multi-task learning capability. Experimental results demonstrated that ALFNet achieved superior joint grading performance on the Messidor dataset, with joint accuracy rates of 0.868 (DR 2 & DME 3), outperforming state-of-the-art methods. These results highlight the unique advantages of the proposed approach in the joint grading of DR and DME, thereby improving the efficiency and accuracy of clinical decision-making.