Due to the advantages of low power consumption, fast response and high measurement accuracy, Micro flowmeter have a wide application in the fields of automotive industry, aerospace engineering, biological research, clinical diagnosis and so on. Calorimetric micro flowmeter determines the flow velocity value by measuring the temperature difference between the upper and lower reaches of heater. However, when the flow velocity exceeds a certain threshold, the temperature difference will not increase with the flow velocity, which limits the measuring range of the micro flowmeter. In this paper, numerical simulations for a wide range of flowrates (0. 01-160 SCCM) are firstly carried out to investigate the response of temperature difference to flowrate. It is found that the response of temperature difference to flow velocity is almost linear when diffusion is dominant. With the increase of flow velocity, the response of temperature difference decreases gradually and is nonlinear. As the flow rate increases further, the response of temperature difference becomes saturated and the calorimetric operation mode fails. Secondly, on the basis of numerical simulation, a dual-mode micro-heat flow sensor is proposed, which adopts hot wire operation mode at high flow rate and calorimetric mode at medium and small flow rate. Finally, a micro flowmeter is manufactured by 0. 18 μm CMOS-MEMS technology, and the threshold for mode-switch is defined by the sensitivity in experiments. Compared with standard flowmeter, the error is less than 2% , which is in line with the practical application requirements, but the range is doubled.