In this paper, a group of GFRP beam-column joints connected with slotted-hole angle steel were analysed under monotonic loading. Based on ABAQUS software, the nonlinear finite element analysis of slotted-hole on beam for GFRP joint and influence of different slotted-hole lengths on mechanical properties of joints were carried out. Considering influence of friction and pretightening force, a conventional circular hole specimen C1 and three specimens K2, K3 and K4 with slotted-hole lengths of 2mm, 4mm and 6mm were designed. The universal contact element and pretension element were applied on ABAQUS finite element modeling of bolted connections. Finally, differences in failure mode, moment-rotation curve, rotational capacity, displacement ductility coefficient and other aspects between angle steel joints with conventional round holes and those with different slotted-hole sizes were compared. The results show that: 1) the rotational capacity of slotted-hole joints was about 6%-19% higher than that of ordinary round-hole joints. The longer the slotted-hole length is, the larger the plastic rotation angle steel will be. However, too large slotted-hole size will also cause excessive deformation of components and collapse.2) The slotted-hole method will not increase bearing capacity of joints, but displacement ductility coefficient of joint K4 with slotted-hole size of 6mm was 1.17 times that of conventional joint C1 with circular hole.