An apparatus of mass flow controlling for use in an integrated gas delivery system, comprising an input terminal, an output terminal, a sensor unit, a flow rate control valve, and a control unit. The control unit comprises an A/D converter, a microprocessor, and a valve control circuit. The A/D converter converts an actual setting signal inputted by the input terminal into a first digital signal, and converts a flow rate detection signal outputted by the sensor unit into a second digital signal. The microprocessor further comprises a storage module, a setting signal calibration module and a calculation module. The valve control circuit generates, based on a control signal, an openness control signal, so as to control the flow rate control valve. It is concluded that the flow rate control quality is improved by the present invention.