A new sensor with optical reflected device using molecularly imprinted polymer film has been investigated. A sensor head employing a medium finesse molecularly imprinted polymer film has been fabricated and characterised. A blank polymer and formaldehyde imprinted polymer were using methacrylic acid as the functional monomer and the ethylene glycol dimethacrylate as a crosslinker. The transduction mechanism is discussed based on the changes of optical intensity of molecularly imprinted polymer film acting as an optical reflected sensor. The formaldehyde molecules that diffuse into the polymer film cause refractive index changes. These refractive index changes induce measurable reflective intensity shifts. By illuminating the molecularly imprinted polymer film with a laser beam,an optical reflection detection of formaldehyde using molecularly imprinted polymers film is demonstrated. This sensor, based on an artificial recognition system, demonstrates long-time stability and resistance to harsh chemical environments. As the work carry out gradually,we establish the possibilities of quantitative analysis primly,setting the groundwork to the synthesis of the molecular imprinted optical fiber sensor。