A three-dimensional (3D) spring-like flow sensor is integrated inside the microfluidic chip by using the femtosecond laser two-photon direct writing technique. The fabricated spring-like flow sensor can be stretched repeatedly for several times, and the deformation is reversible. In addition, different laser exposure powers can be adopted to fabricate the spring-like flow sensors with different thicknesses, and thus flow rates within different ranges can be monitored and the minimum flow rate which can be monitored is at 10-12 level. This flow sensor can be used in many kinds of microfluidic devices, especially in situations where the flow rate detection is required to be combined with other microfluidic devices and in the ultralow flow rate detection.