A unified national carbon market is crucial for facilitating the optimal resource allocation, balancing low-carbon economy development and achieve the double goals of total carbon emissions with carbon intensity. Based on Guangdong carbon market, the paper explores as follows: Firstly, we summarize the practice of Guangdong carbon market, including controlling carbon intensity - the increase of applied baseline method and baseline standards, and carbon emissions - the set of cap and the restraints of industrial and regional emissions; Secondly, the analysis focuses on six problems in Guangdong carbon market, i.e. lack of systematicness and scientificalness in top-level design, scarcity absence of carbon quotas, loss of cost effectiveness in carbon market mechanism, no significant price guidance of the primary market to the secondary market, less attentions of enterprises and low proportion of CCER in carbon compliance; Finally, combined with the practices of Guangdong and developed countries carbon markets, we put forward with the corresponding policy proposal in the establishment of unified national carbon market.