[11] applied a Super-SBM DEA considering the undesirable outputs to measure the integrated transport efficiency (ITE) of 31 provinces in China during the period of 2009-2016. [PERSON] et al. [12] studied the scale and efficiency of cassava planting using the output-oriented DEA model. However, conventional DEA deals with one-stage production processes, where the internal structure of the DMUs is not taken into account and each DMU as a \"black box\" by considering only the inputs consumed and outputs produced [13]. The Network DEA (NDEA) paradigm refers to multi-stage processes, where the underlying structure, which indicates the flow of the intermediate measures among the stages, plays a key role in the efficiency assessment [14; 15; 16]. The network DEA method is widely used in various fields. [PERSON] et al. [17] studied the efficiency of China's listed commercial banks based on a three-stage process where the number of workers, operating expenses, and fixed assets are used to generate deposits and deposit taking of interbank in the first stage, and then the investment securities, loans, and due from banks are produced in the second stage by using the intermediate premiums as a resource. Those second stage outputs are then used as third stage input resources to output the net profit and normal loan rate. [PERSON] et al. [18] measured the efficiency of supporting agriculture of China's Rural Credit Cooperatives based on a two-stage process. In their paper, the first stage is called the operating activities process, which uses inputs of the number of workers and total assets to produce outputs of the balance of loans relating to agricultural supporting. Those first stage outputs are then used as second stage input resources to output the added value of primary industry and township enterprises, and rural per capita net income. [PERSON] et al. [19] applied the two-stage Network DEA to 64 Chinese research universities and their evolution over the period of 2010-2013. However, [PERSON] et al. [20] indicated that resource sharing exists, not only among multiple entities, but also among various stages of a single network structure system. They integrate cooperative game theory with network data envelopment analysis (DEA) to explore the payoff allocation problem in a three-stage system. [PERSON] et al. [21] improved the two-stage network DEA methodology to determine the relative efficiency while taking the internal structure and possible allocated costs into account. Recently, some further studies of DEA method have begun to involve sustainability. The same two-stage process has been applied in environmental sustainability evaluation contexts ([PERSON] [22]; [PERSON] [23]; [PERSON] [24]; and, many others). More detailed reviews of DEA method applying in sustainability can be seen in [PERSON] et al. [25]. Packaging systems have multi-stage characteristics throughout the overall life cycle, so that the conventional DEA has poor applicability to the packaging system. In this paper, first, the overall packaging system life cycle has been divided into three stages. Subsequently, a three-stage NDEA model is constructed to compute the PSI. The PSIs have been used to evaluate the environmentally friendly of the packaging system in its overall life cycle, and the ideal results are obtained. Finally, we use the PSI to make an empirical study on the environmental performance of three types of milk packaging system and obtain satisfactory results.