The second-phases have a significant impact on the pitting behaviors of laser powder bed fusion (LPBF) high strength stainless steel. The size, composition and interface characteristics of multiscale second-phases and effects on the pitting mechanisms were studied in this paper. The results showed that there were Si-rich irregular inclusions, spherical oxides inclusions, NbS/NbS-Mn particles and 3–5 nm (Cu, Nb)-rich precipitates for LPBF high strength stainless steel. The surface potential of the irregular inclusions was 67 mV higher than that of martensite and the obvious microcracks or gaps at the interface between irregular inclusions and matrix were observed. The pitting resistance and electrochemical impedance value of LPBF high strength stainless steel was lower than that of conventional samples due to galvanic corrosion and the gap defect for high content of irregular inclusions.