Concerns about China’s energy security have escalated because of the country’s high dependency on oil and gas imports, so it is necessary to calculate the availability of domestic oil and gas resources and China’s ability to obtain foreign energy through trade. In this work, the calculation was done by using the energy return on investment (EROI) method. The results showed that the EROI_stnd (i.e., standard EROI) of China’s oil and gas extraction decreased from approximately 17.3:1 in 1986 to 8.4:1 in 2003, but it increased to 12.2:1 in 2013. From a company-level perspective, the EROI_stnd differed for different companies and was in the range of (8–12):1. The EROI_2,d (EROI considering energy outputs after processed and direct energy inputs) for different companies was in the range of (3–7):1. The EROI of imported oil (EROI_IO) declined from 14.8:1 in 1998 to approximately 4.8:1 in 2014, and the EROI of imported natural gas (EROI_ING) declined from 16.7:1 in 2009 to 8.6:1 in 2014. In 2015, the EROI_IO and EROI_ING showed a slight increase due to decreasing import prices. In general, this paper suggests that from a net energy perspective, it has become more difficult for China to obtain oil and gas from both domestic production and imports. China is experiencing an EROI decline, which demonstrates the risk in the use of unsustainable fossil resources.