A series of polysulfone-based crosslinked anion exchange membranes (AEMs) with primary diamine-based crosslinkers has been prepared via simple a crosslinking process as low-cost and durable membranes for vanadium redox flow batteries (VRFBs). Chloromethylated polysulfone is used as a precursor polymer for crosslinked AEMs (CAPSU-x) with different degrees of crosslinking. Among the developed AEMs, CAPSU-2.5 shows outstanding dimensional stability and anion (Cl−, SO4 2−, and OH−) conductivity. Moreover, CAPSU-2.5 exhibits much lower vanadium ion permeability (2.72 × 10−8 cm2 min−1) than Nafion 115 (2.88 × 10−6 cm2 min−1), which results in an excellent coulombic efficiency of 100%. The chemical and operational stabilities of the membranes have been investigated via ex situ soaking tests in 0.1 M VO2 + solution and in situ operation tests for 100 cycles, respectively. The excellent chemical, physical, and electrochemical properties of the CAPSU-2.5 membrane make it suitable for use in VRFBs.