With development of theory on microalloy in steel, now there are trends of adding microalloy in many kinds of steels, making the production and application of microalloy-steel enlarge. The second phase in microalloy-steel is significant for quality of casting. During the periods of continuous casting, conveying and heating, different process may affect precipitation and dissolution behaviors of casting according to different heating profile, further affect state of precipitation and distribution of secondary phase. In this paper, secondary phase in micro-alloy steel J55 were studied. Results show that some secondary phase particulars in micro-alloy steel J55 steel distribute along the austenitic grain boundaries when the temperature of slab is below 805°C in roller conveying; The distribution of secondary phase particulars in different thermal history slab are comparatively similar after heating; Al, Ti, C and N elements which dissolute in J55 steel has the feature of austenitic grain boundary segregation.