Whether or not China can succeed at the forefront of international development in the coming decades will largely hinge on its ability to adapt to low-carbon economic development and its efforts to promote the Unified National Emission Trading System (UNETS). To understand the evolution of China’s carbon market, this paper firstly divides the development of China’s regional carbon markets into three phases: pilot construction (phase 1, before 31 May 2015), preparation for the UNETS (phase 2, 1 June 2015–19 December 2017), and formal construction of the UNETS (phase 3, 20 December 2017–present). Then this research reviews the trading performance and employs four robust variance ratio (VR) tests to capture structural changes and examine the efficiency of China’s eight regional carbon markets in different periods. Results show that compared to phase 1, smaller price volatility, larger daily trading volume, and higher market liquidity are more frequent at the later stages of majority markets. Despite these improvements, results from the VR tests indicate that the statistic in majority of China’s regional carbon markets is insignificant in any given period and, therefore, they are not weak-form efficient. The additional detrended cross-correlation analysis demonstrates that market liquidity affects market efficiency in the Hubei market only, which implies that Hubei, where the market liquidity reaches almost 100% in phase 3, is highly likely to be weak-form efficient shortly. Finally, several recommendations are provided to improve the efficiency and maturity of China’s carbon markets, including strengthening legislation, improving the market design, and constructing information platforms.