This study proposes a new approach to measure the dynamic importance of environmental technologies with patent co-classification information. First, patent co-classification analysis is applied to construct co-classification matrices from the frequency, relatedness, and cross-impact perspectives. Second, the analytical network process is used to the constructed co-classification matrices to determine the priority values of environmental technologies, taking into account their direct and indirect relationship. Finally, date envelopment analysis window analysis is employed to the derived priority values to examine the dynamic changes of the environmental technologies’ importance, reflecting three co-classification perspectives together. The proposed approach can be utilized for both environmental technology planning and eco-innovation policy making.