The invention discloses a ferroelectric tunnel junction room-temperature infrared detector and a preparation method. The ferroelectric tunnel junction room-temperature infrared detector is characterized in that a substrate, a metal bottom electrode, a ferroelectric function layer and a metal semi-permeable top electrode are sequentially arranged in a detector structure from bottom to top. Preparation steps of the detector include evaporating or sputtering metal on the surface of a flexible film substrate to be used as the bottom electrode; then growing a PVDF (polyvinylidene fluoride) base polymer film with the thickness ranging from 1 nanometer to 6 nanometer on the surface of the bottom electrode by the aid of an LB (Langmuir Blodgett) method to be used as the ferroelectric function layer; preparing the metal top electrode on the ferroelectric function layer by the aid of an evaporation or sputtering method to form a ferroelectric tunnel junction; and finally thinning the substrate. The detector realizes infrared detection by means of leading in tiny constant current and measuring voltage at two ends of an electrode in an illumination environment. The detector has the advantages that the temperature coefficient and the polarities can be adjusted according to requirements of application environments and detected targets, incident radiation modulation is omitted, and the like.