A slow neutron detector, comprising: a slow neutron converter; a cathode plate, disposed at one end of the slow neutron converter; an electron multiplier, disposed at another end of the slow neutron converter; and an anode plate, disposed opposite to the electron multiplier, an electric field being formed between the cathode plate and the anode plate, wherein the slow neutron converter comprises: a substrate, comprising a plurality of holes extending along a first direction; and a boron layer, at least covering an exposed surface of the plurality of holes; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter, characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage. a slow neutron converter; a cathode plate, disposed at one end of the slow neutron converter; an electron multiplier, disposed at another end of the slow neutron converter; and an anode plate, disposed opposite to the electron multiplier, an electric field being formed between the cathode plate and the anode plate, wherein the slow neutron converter comprises: a substrate, comprising a plurality of holes extending along a first direction; and a boron layer, at least covering an exposed surface of the plurality of holes; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter, characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage. a substrate, comprising a plurality of holes extending along a first direction; and a boron layer, at least covering an exposed surface of the plurality of holes; wherein the plurality of holes are through holes, the substrate further comprises insulating walls between the plurality of holes; the substrate has a height in the range of 10 cm to 15 cm along the first direction; the plurality of holes are filled with an ionization working gas to produce electrons; and the slow neutron detector further comprises a field cage having a cylindrical structure, wherein the field cage surrounds the slow neutron converter, characterized in that the ionization working gas is a mixed gas having 95% argon gas and 5% carbon dioxide gas; and the slow neutron detector further comprises protection rings disposed on both sides of the field cage.