Dissolved organic matter (DOM) in the ocean is involved in remineralization, nutrients supply as well as carbon sequestration by bacteria utilization and alteration. During the degradation process, DOM might show different composition because of the different bio-availability of DOM (labile DOM, semi-labile DOM, and refractory DOM). In July 2017, We collected 61 SPE-DOM samples on SCS-Luzon Strait summer cruise and chose 20 samples to do FT-ICR-MS (Fourier-transform ion cyclotron resonance mass spectrometr) analysis. The results indicate that there are a lot of similar molecular structures exist in all SPE-DOM no matter where the samples are collected from, which means those molecules might be refractory DOM. Also, we observe the degradation process of DOM between 5m and 3500m through the disappearance of high O/C and H/C part where is the region of carbohydrate, amino acid, and sugar. It suggests a preference of bacteria degradation for labile DOM. However, the surface and deep samples share more than 70% peaks on the mass spectrum; and two surface samples collected from different areas share more than 80% peaks on ESI- mode. Most of the overlapping peaks locate in 'CRAM' (carboxyl-rich alicyclic molecules) region on Van Krevelen Diagrams. Furthermore, we are trying to use HPLC-QTOF -MS to do the same samples and compare with FT-ICR-MS to see different characterization information from HPLC and daughter ion spectrum, and the work is underway.