The relaxor-based manganese iron doped lead magnesium niobate/lead titanate (Mn∶Pb(Mg1/3-Nb2/3)O3-PbTiO3, Mn∶PMN-PT) ferroelectric single crystal has a high light transmittance in the near/mid-infrared band. The pyroelectric infrared detecting element was prepared by depositing an infrared absorption layer with broad spectrum and flat absorption characteristics on its surface. The temperature difference and pyroelectric current change with frequency caused by the absorption of infrared radiation were simulated. The response characteristics and influencing factors of the voltage mode pyroelectric detector were discussed. Furthermore, a dual-channel compensated pyroelectric infrared detector based on Mn∶PMN-PT single crystal was prepared. The frequency response results obtained in the experiment are in good agreement with the simulation, and are suitable for gas detection based on the principle of non-dispersive infrared (NDIR).