The Mn‐Co‐Ni‐O thin film thermo‐sensitive infrared detector has important application prospects and still need further research and development. The effects of substrate thickness and probe element spacing on the detector thermal conductivity are studied in this paper to improve the performance of linear and planar array infrared detector. It is found that the thermal conductivity of fabricated detector mainly rely on the Cu socket for thin substrates. However, the heat is mainly transferred by Al2O3 substrate and the influence of Cu socket can be ignored for thick substrates. The decrescent probe element spacing will reduce the effective thermal conductivity Ge for infrared detectors. Both of the time constant τ and the responsivity will increase with the expansion of element area. For the responsivity, its alterations are mainly affected by the changes of Ge value for the chopping frequency f less than 20 Hz. Comparably, the alternations are affected by the changes of Ge, f, τ values in 20–64 Hz and Ge, f values above 64 Hz.