With the improvement of the development level of cooled infrared detectors, the demand for low heat leakage has been put forward for the dewar structure. Through mechanical simulation and theoretical analysis of conduction heat load, a design of cold finger structure with gradient wall thickness for low heat load infrared detectors is proposed, and the influence of the outer diameter gradient position of the cold finger with gradient wall thickness on mechanical reliability and conduction heat leakage is explored. The results show that if a large-scale vibration condition is adopted, the outer diameter gradient position of the cold finger with gradient wall thickness can be appropriately moved up to enhance the stability of the structure; if a small-scale vibration condition is adopted, the outer diameter gradient position can be appropriately moved down. Under the premise of meeting mechanical reliability, the heat load is further reduced, and the component optimization verification is carried out. Under the premise of ensuring mechanical reliability, this structure can reduce the static heat load of the dewar by 15% to 18%.