The invention discloses a neutron radiography detection method for a residual core of a hollow turbine blade cavity. The method comprises the following steps that distilled water is prepared by utilizing purified water; the distilled water is contained by a special plastic water container; a hollow turbine blade is horizontally placed and completely immersed into the distilled water for 5-10min; a water level is kept to be slightly higher than the horizontal placing height of the blade; the plastic water container is loaded into a freezing chamber for continuous cooling; the temperature is controlled to be -10-30 DEG C; the plastic water container is taken out after complete freezing; the blade is taken down; an ice cake on the surface of the blade is removed; residual flake ice and water stains on the surface of the blade are cleaned by dry water absorption cloth; and the blade is loaded into a neutron radiography detection chamber. An attenuation coefficient of a core material to a thermal neutron ray is far less than an attenuation coefficient of ice to the thermal neutron ray, so that thermal neutron radiography detection of the residual core can be performed. The thermal neutron radiography detection method for the residual core is simple to operate and high in residual core detection rate, and is applicable to a neutron film radiography method and a real-time imaging method.