The speciation analysis of cadmium in seaweed(including Porphyra haitanensis, Laminaria japonica,Undaria pinnatifida and Sargassum fusiforme)was firstly conducted using sequential chemical extraction considering that high content of cadmium in some seaweed had seriously affected the edible safety,export and industry development of seaweed in our country.The results showed that many forms of cadmium were in the four kinds of seaweed,and the greatest amount of cadmium was in the extraction of 1 mol/L NaCl,followed by 2% HAC and both forms accounted for 76.3%-92.9% of the total cadmium.The cadmium content in the extraction of 0.6 mol/L HCl,deionized water and 80% ethanol was much smaller.80% ethanol could extract the ionized cadmium(Cd²⁺)which only accounted for 0.4%-9.2% of the total cadmium,and especially for laver,ionized cadmium was all bellow 1%.Present experiment further proved that using total cadmium content as the detection standard could not accurately reflect the edible safety of the seaweed,so a more accurate limit standard and a quick detection method of the ionized cadmium for seaweed should be urgently researched and established in order to guarantee the fast development of the industry and export economy of the seaweed in China.