The invention relates to a microfluid tunable optical filter based on a PDMS (Polydimethylsiloxane) chip and a manufacture method thereof. The microfluid tunable optical filter comprises a spontaneous radiation light source, a PDMS microfluid chip with double microchannels, a spectrograph and two groups of injection pumps working independently, wherein the light incident end and the light emergent end of the microfluid chip are respectively connected with the spontaneous radiation light source and the spectrograph by coupling optical fibers respectively, a first fluid injection end and a second fluid injection end of the microfluid chip are respectively connected with two groups of injection pumps working independently; when a fluid is injected in a T-shaped channel structure, the required fluid injection pressure is low, the liquid is difficult to splash and the performance is stable; two kinds of fluids are diffused and mixed in a horizontal channel, the longitudinal liquid refractive index gradient is obvious and the sensitivity is high; and the microfluid tunable optical filter can be integrated in an optical flowing control chip, can be conveniently applied to sampling in real-time biological and environment monitoring without influencing observation and recording of an interference curve, and is beneficial to laminar stability to obtain stable signals.