A chemical liquid dilution system includes a first material offering device providing fluid, a second material offering device, and a mixing device. The second material offering device provides liquid. The mixing device includes a fluid mixer, a first connection port, a second connection port, and an output port. The fluid mixer has a fluid limiting channel with an interface communicating with the first connection port and another interface communicating with the second connection port and the output port. The first connection port is connected to the first material offering device. The second connection port is connected to the second material offering device. After the fluid passes through the first connection port and the fluid limiting channel, the fluid and liquid are mixed up to form a diluted chemical liquid, and the output port discharges the diluted chemical liquid. A chemical liquid dilution method is also disclosed.