Blocked Impurity Band （BIB） detectors have significant application potential in fields such as infrared astronomical space observation. However， studies on their temperature-dependent mechanisms remain limited. In this work， a planar p-i-n structured BIB infrared detector based on high-purity germanium was fabricated using a near-surface processing technique. The device exhibited excellent electrical and photoresponse performance under cryogenic conditions. At 3.3 K， the reverse bias current was as low as 15 pA， and good response was maintained below 15 K. The blackbody detectivity reached up to ， but decreased with increasing temperature. A current model incorporating photoexcitation， thermal excitation， and impact ionization processes was employed to simulate the experimental results. The analysis revealed that the primary mechanism for performance degradation at elevated temperatures is the significant shrinkage of the depletion region， which reduces carrier collection efficiency. This study provides both theoretical and experimental support for the structural design and performance optimization of BIB detectors for low-temperature infrared detection.