Laser scanning confocal microscopy(LSCM) was used to study the inhibition of austenite grain growth by the inclusions and the effect of cerium on the trend of acicular ferrite(AF) and ferrite side plate(FSP) transformation temperature in coarse grain heat affected zone(CGHAZ) of Ce-alloyed weld metals. The results showed there were lots of tiny cerium oxides and sulfides inclusions in the CGHAZ of Ce-alloyed weld metals. When the concentration of Ce was 0.021%, the volume fraction of inclusions in weld metal CGHAZ was higher and the inclusion size was smaller, therefore austenite grain size was smaller with the increase of hightemperature residence time. Cerium tended to segregate at austenite grain boundaries, so FSP transformation temperature decreased and FSP transformation was suppressed. On the contrary, AF transformation temperature increased because AF transformation was promoted in CGHAZ of the Ce-alloyed weld metal, especially when the concentration of Ce was 0.021%. Laser scanning confocal microscopy (LSCM) was used to study the inhibition of austenite grain growth by the inclusions and the effect of cerium on the trend of acicular ferrite (AF) and ferrite side plate (FSP) transformation temperature in coarse grain heat affected zone ( CGHAZ) of Ce-alloyed weld metals. The results showed there were lots of tiny cerium oxides and sulfides inclusions in the CGHAZ of Ce-alloyed weld metals. When the concentration of Ce was 0.021%, the volume fraction of inclusions in weld metal CGHAZ was higher and the inclusion size was smaller than the increase of hightemperature residence time. Cerium tended to segregate at austenite grain boundaries, so FSP transformation temperature decreased and FSP transformation was suppressed. increased because AF transformation was promoted in CGHAZ of the Ce-alloyed weld metal, especially when the concentration of Ce was 0.021%.