To solve the problem of the rapid startup of detectors, a systematic study is conducted on the factors affecting cooling of the cooling head structure. The cooling capacity of cooling head required for the temperature reduction of the cold-head structure is calculated, and a thermal network model is established according to the actual heat transfer path of the cooling head. The thermal resistance of cooling head is computed and analyzed, indicating that the thickness of cold shield affects both the cooling capacity needed for temperature reduction and the thermal resistance. These two factors are in conflict with each other, and there exists an optimal value for them. Through finite element simulations, calculations are carried out for different cold-head structures, cold-shield wall thicknesses, and adhesives. As a result, the optimal parameters for the cold-head structure in fast-startup detectors are determined, and targeted optimization designs are proposed.