The invention discloses a boron carbide shielding block for spallation neutrons. The boron carbide shielding block comprises a neutron generating box, a conveying pipe, an adjusting pipe, an adjuster,an upper interlayer, a lower interlayer, a gas port, a push rod, a diaphragm, a backspring, a partition plate, an isolation layer, a cooling liquid circulator, a boron carbide shielding block body and a neutron outlet. The neutron generating box is connected with the adjusting pipe through the conveying pipe, the adjuster is mounted above the adjusting pipe, the gas port connected with a gas compressor is formed in the top of the adjuster, the push rod is mounted in the adjuster, the push rod stretches to the adjusting pipe to be connected with the boron carbide shielding block body, the partition plate is mounted at the bottom of the lower interlayer, the isolation layer is mounted below a test layer, the cooling liquid circulator is mounted below the isolation layer, the boron carbide shielding block body is arranged below the cooling liquid circulator, the boron carbide shielding block body is mounted on the adjusting pipe and connected with the push rod, and an upper guide plate and a lower guide plate which incline inwards are mounted on the portions, on the two sides of the boron carbide shielding block body, in the adjusting pipe.