Abstract: For DD5 single crystal superalloy blade of the Aeroengine, the stepped reference sample and blade reference samples were designed and prepared by gadolinium doping method. Using cold neutron source and imaging method of single-emulsion industry film, the detection sensitivity of residual core with Gd₂O₃ tracer content of 3% was studied. The quantitative relation among sensitivity, transmission thickness and residual core thickness, as well as the influence of blade structure on detection results were analyzed. The results show that the spatial resolution of the combination of cold neutron source and single-emulsion film is up to 50 μm. With the decrease of transmission thickness and the increase of residual core thickness, the detection sensitivity of residual core increases gradually. The results provide a reference for the practical application of hollow turbine blade, proves that the cold neutron photography testing has good applicability, which can achieve the high detection sensitivity of residual core.