Selective laser melting (SLM) or laser powder bed fusion (LPBF), is one type of metal additive manufacturing (AM) technology which is efficient in producing lightweight hydraulic components. However, the fabricating quality is poor when flow channels are built horizontally on the substrate due to residual stress on the large overhang region. Large surface roughness and dimensional error occurs which greatly affect friction factor but not studied. In this work, fluid channels with various diameters were built using SLM. The surface roughness and profile were characterized. Friction factor was then measured using a customed test rig. Results indicate that SLM fabricated fluid passages have high and uneven roughness and dimensional accuracy is poor. A new friction factor model was developed which can be used to calculate pressure loss in a SLM fabricated fluid channels.