The formation process of alternating droplets at the T-junction with a cross-sectional area of 400 mu m x 400 mu m was investigated using a high-speed camera. The alternating droplets were consisted of glycerol aqueous solution and ferrofluid droplets. Two formation types of alternating droplets were observed: normal formation and the upstream droplet squeezing formation. The existence of the magnetic field delayed the transition from the normal farmation to the upstream droplet squeezing formation. The effects of two-phase flow rate and magnetic flux density on the dynamics of the tip and the neck of the ferrofluid and the formation period were studied. The results show that the neck evolution of ferrofluid could be divided into the expansion stage and pinch-off stage. The expansion stage was dominated by the flow of ferrofluid, and the pinch-off stage was insensitive to fluid flow and was a self-similar process. The length of the tip of ferrofluid increases almost linearly with time during the pinch-off stage, and the increasing rate rose with the flow rates. The formation period of the droplets reduces as the fluid flow rate increases. When the formation type is normal formation, the existence of the magnetic field shortens the formation period. When the formation type is the upstream droplet squeezing regime, the existence of the magnetic field prolongs the formation period. This paper provides a new method for the generation of alternating droplets. (C) 2019 Elsevier Ltd. All rights reserved.