The broth and pan-fried soup(PFS)of tuna (Thunnus obesus)head were stewed by two different methods. Fatty acid compositions and vitamin E (V_E) contents of two different tuna head soups were analyzed and its microscopic morphology were observed during the cooking process. The results showed that there were 22 kinds of fatty acids both in the broth and PFS. The proportion of saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids and V_E reached the maximum with the condition of fish to water ratio of 1:8(m/m), boiled for 150 min, and the contents in the PFS were higher than those in the broth.The average particles size of the micro/nano-size particle in broth and PFS after microfiltration and ultrafiltration treatment was measured by Malvern laser particle size analyzer, and it was found that the average particle size of the two kinds of soup was significantly smaller (P<0.05), but re-aggregation occurs to form larger particles. Observed under Inverted microscopy microscope, the particles were found to be unequal-sized spherical, with wide size distribution and good dispersion.This paper provides a research basis for the transfer of nutrients into the soup during the cooking process. Furthermore, it provides theoretical basis for the production of high-quality fish soup.