Sustainability is a crux for the future development of wastewater treatment technologies. Especially under the condition where the Paris Agreement concerning climate change was settled down, energy consumption will determine the future development of sustainable technologies to a large extent. In this case, technology of membrane bioreactor (MBR), which has been debated extensively at home and abroad, has to be quantitatively evaluated to conclude a comprehensive benefit on their merits and demerits in economy, society and environment. Based on establishing an evaluation index model (S_I) for the sustainability of MBR processes, capital and operational cost, processes' effect and their reliability, and resource recovery and utilization were elaborated, and all related parameters and their reasonable ranges in the established model were analyzed and identified. The calculated results of the model revealed that the sustainability of MBR processes was not as good as conventional activated sludge processes. In other words, MBR is basically not a sustainable process, as the high energy consumption and operational cost have totally shield their merits on good effluent quality and small footprint.