Polymer-based composite films represent a promising approach for developing recyclable catalysts. In this study, a [Fe(NH2trz)3](NO3)2 @TPU composite film with spin crossover properties was fabricated using the blade casting method. Various characterisation techniques confirmed the uniform distribution of [Fe(NH2trz)3](NO3)2 particles within the TPU matrix, while maintaining the spin-crossover properties of the embedded complex. The composite film exhibited excellent catalytic efficiency and reusability in acetalization reaction, enabling efficient catalysis for up to 11 cycles under batch conditions and sustained activity for 7 hours under flow conditions. In addition, the color of the film served as a convenient visual indicator of its suitability for reuse in subsequent catalytic reactions. This study demonstrates that [Fe(NH2trz)3](NO3)2 @TPU composite film can serve as an effective and recyclable catalysts for acetalization reactions.