In terms to the selection of valve spool material in the vibration displacement detection to the core valve spool of the pilot relief valve, this paper researches and determines the materials of the core valve spool are researched and determined from two aspects, including the influences of different materials on the detection performance of the sensor and on the mechanical properties of the core valve spool. Ansoft Maxwell was firstly used to research the effects of four different materials on the eddy current testing. And then the change law of the coil impedance that follows with the detection distance and its applicability to the transformer type equivalent circuit were analyzed. Next the mechanical properties of the core valve spool of the four different materials were researched, which analyzed and compared the stress, the deformation distribution, the life expectancy and the safety factor of the core valve spool. And finally the material of the core valve spool was selected. The results show that the aluminum alloy material can be used in eddy current testing and it is suitable for transformer type equivalent circuit, which meets the mechanical property requirements of the core valve spool, therefor it is selected as the core valve spool material.