In order to explore the changes of total polysaccharide, mannitol and algin content of fresh kelp under drying conditions, grasp its drying characteristics and establish a drying model that can accurately predict the drying process. The wet base moisture content of kelp reaches less than 18% as the drying end point. It is analyzed that the kelp in the Rongcheng sea area of Shandong Province is dried under the condition that the light intensity is greater than 30 000 Lx and the relative humidity is less than 70% in Shanghai from June to July. Changes in the content of alcohol and algin, and the kelp drying model was established by fitting six drying mathematical models. The results show that the root thickness of kelp is different, but the initial moisture content is similar, which is between 88% and 92%. The drying process is mainly divided into adjustment stage, fast precipitation stage and slow precipitation stage, and the drying rate goes through two stages of acceleration and deceleration. Different fresh kelp had different initial total polysaccharide, mannitol and algin content. After long-term drying, the total polysaccharide content decreased the most, followed by alginate, and mannitol changed the least. Using six common drying mathematical models to fit and analyze, the mean value of Page model R2 is 0.990, and the mean value of root mean square error RMSE is 0.022 4, which can best describe the moisture change of kelp during drying. A set of data outside the modeling was selected for verification analysis, and the correlation coefficient between the simulated and measured MR values was 0.995 (P<0.05), and the two were significantly correlated, indicating that the model can relatively well describe the natural drying of fresh kelp. Changes in moisture content over time during drying. The research results can provide a theoretical reference for the later joint drying research with heat pump.