Abstract: The effect of Cu on effective grain size of deposited metal in HSLA steel was investigated by TEM and EBSD. Experiment results indicated that microstructure of deposited metal was composed of lath bainite and lath martensite, increase of Cu content from 0.052% to 0.53% resulted in refining of lath configuration. When Cu content was 0.052%, the mean size of effective grain was 2.39 μm. When Cu conted was increased to 0.24%, it was 2.18 μm. When it continued to increase to 0.53%, the mean effectiue grain size was 1.99 μm. With the increase of Cu content, the effective grain were refined.Highlights: (1) Relationship between Cu content in the deposited metal and effective grain size was studied.(2) Applied EBSD technology to statistics of size of effective grain of deposited Metal in HSLA.(3) High grade of steel was studied.