Insufficient grouting of sleeve connection in precast concrete (PC) structure will significantly decrease the bearing capacity of connection joints and increase the risk of premature failure of PC structures. To evaluate the bond behavior of insufficiently grouted sleeve connection, a total of 126 specimens with four types of insufficient grouting configuration (uniform, longitudinal, radial and inclined) have been experimentally investigated. The influences of the configuration and defect level of insufficient grouting on the bond failure mode and bond stress-slip curves were analyzed. The test results show that the specimens fail in the shifting failure mode from the tensile fracture of rebar to the pulling out of rebar with the increase of defect level for all types of grouting defects, especially when the defect level excesses 30%. Moreover, the bond strength and the slip are found to decrease with the increasing of defect level, and empirical expressions have been presented for both the normalized bond strength and slip. Finally, a bond stress-slip constitutive model has been proposed considering the failure modes under different defect levels, which is helpful to the assessment of structural performance of PC structures in practice.