The ductility of high strength steel (HSS) is not as good as mild steel, so that it does not meet the ductility requirement of seismic design. Consequently, the hybrid connection between mild steel and HSS shall be used in the structural design to meet the seismic requirements. In order to evaluate the slip performance of hybrid connections between high strength steel and mild steel, 30 specimens were fabricated from HSS (Q550, Q690 and Q890) and mild steel (Q235 and Q345) to test the slip factors of shot-blasted surface. The test results of slip factors from the 30 specimens were compared with the measured ones from connections with the same steel grade of HSS. According to the test results, the slip factors of hybrid connections are higher than those of connections fabricated by the same grade of HSS plates. In design, it is recommended to take the value of slip factor for hybrid connection the same as that of the connection fabricated by the same grade of HSS plates. The slip factor of 0.50 is recommended for hybrid connections between Q550 and mild steel, while for hybrid connections between Q690 (Q890) and mild steel, the slip factor of 0.45 is recommended. Moreover, the hardness, roughness and deformation capability for the same batch of steels were measured to evaluate the effect of steel grade on the slip factor. It is indicated that the slip factor shall be affected by not only surface roughness but also plastic deformation capacity. The deformation capacity depends on both steel plasticity and the difference between steel grades of hybrid connection. With the increase of steel grade, the slip factor of hybrid connection tends to decrease due to the reduction of surface roughness and steel plasticity.