A calibration system for calibrating pressure sensor comprises communication pipe, base, inlet valve, outlet valve, pump, inlet pipe, heater and reference pressure sensor. The communication pipe has first and second openings. The base comprises chamber body and outlet being disposed at the chamber body. The inlet valve is disposed at the first opening. The chamber body is connected to the second opening so as to define a space between the inlet valve and the outlet valve. The heater is to heat a fluid in the space. The reference pressure sensor is configured to measure a pressure of the fluid. The at least one target pressure sensor is detachably mounted on the chamber body via the base so as to measure the pressure of the fluid in the space.