A monolithic integrated pressure-flow sensor with on-chip signal-conditioning CMOS circuit has been developed for simultaneous measurements of pressure and flow rates, which is used in automatic control system. Both the pressure sensing and flow sensing are based on the piezoresistive effect, and only one additional mask is applied on the integrated pressure sensor to realize the pressure-flow sensor. A fully integrated pressure-flow sensor, which is based on inter-COMS process, is fabricated and packaged. A commercial computational fluid dynamics (CFD) software package, Fluent 6.1, is used to model the flow inside this pressure-flow sensor. The performance of the sensor is then predicted utilizing Coventorware based on the result from CFD simulation. For the testing, pressure sensor was first calibrated at the range of 0-50 KPa, and it showed a pressure sensitivity of 1.3 mV/mmHg. Afterwards, the simultaneous measurement of pressure and flow rate is implemented at air flow rates of 0-5 L/min. Both the pressure output and flow output have a quadratic relation with the input flow rate of the fluid, which is consistent with the simulation results. Based on the pressure calibration, the dependence of pressure to flow rate is finally obtained.