The price of carbon emission trading in China has obvious volatility and regional differences. Scientifically describing the volatility of carbon emission trading price and analyzing the differences of different regions are conducive to avoiding investment risks, developing carbon market smoothly and improving the pricing ability of domestic carbon market in the international market. It is also particularly important to speed up the establishment of a unified national carbon market. H-P filtering is a commonly used trend decomposition method for economic variables, which can effectively analyze the seasonal variation law in time series data. Based on monthly data of carbon emission trading prices in seven major regions of China from December 2013 to June 2018, H-P filtering method is used to empirically study the fluctuation law and regional characteristics of domestic carbon prices. The results show that the domestic carbon price has a significant characteristic of "falling in fluctuation", showing 3 complete cycles, the time range of each cycle is 10~22 months. Peak and valley values show a downward trend in varying degrees, and all of them change from positive to negative, the cycle types show a steep downward trend. From the regional perspective, the volatility of carbon emission trading price in Tianjin and Beijing is more obvious, while the fluctuation of carbon emission trading price in Hubei and Chongqing has less impact on Tianjin.