An adjustable coolant quick coupler has a coolant supplier seat and a transmission seat that can be optionally connected or disconnected. The coolant supplier seat has a regulator assembly. The regulator assembly is able to adjust quantity of flow-in coolant and quantity of flow-out coolant. When the coolant supplier seat is connected to the transmission seat, the coolant can flow automatically from the coolant supplier seat to the transmission seat, so as to cool down electronic components inside a rack. When the coolant supplier seat is disconnected from the transmission seat, the coolant instantly stops flowing into the transmission seat. Because of the quick coupler, the rack installed inside a narrow space is convenient to set up or disassemble. Furthermore, by adjusting the quantity of flow-in coolant and the quantity of flow-out coolant, the electronic components can have a better effect of heat-dissipation.