A flat plate type solid oxide fuel cell stack unit, comprising: an anode plate, formed as a rectangle, having a first flow channel structured on a surface thereof, four first fuel input holes located respectively to four corners thereof, and a first fuel output hole located at a center thereof; a cathode plate, shaped as a rectangle, having a second flow channel structured on a surface thereof, four second fuel input holes located at respective corners thereof, a second fuel output hole located at a center thereof, a plurality of second air input grooves disposed along a lateral side thereof, and a plurality of second air output grooves disposed along another lateral side thereof opposing to the lateral side, wherein the second air input grooves, the second air output grooves and the second flow channel are all communicative in space; a cell unit, shaped as a rectangle, having four third fuel input holes located at respective corners thereof, a third fuel output hole located at a center thereof, a cathode layer disposed at one side thereof to face the second flow channel, an anode layer disposed at another side thereof opposing to the side to face the first flow channel, wherein the four first fuel input holes, the four second fuel input holes and the four third fuel input holes are aligned respectively in positions, wherein the first fuel output hole, the second fuel output hole and the third fuel output hole are aligned respectively in positions; an anode metal net, located between the anode plate and the cell unit; a cathode metal net, located between the cathode plate and the cell unit; at least one anode sealing material, disposed between the anode plate and the cell unit to surround the first fuel input holes, the first fuel output hole, the first flow channel, the cell unit and the anode metal net; and at least one cathode sealing material, disposed between the cathode plate and the cell unit to surround the second fuel input holes, the second fuel output hole, the second flow channel, the cell unit and the cathode metal net. an anode plate, formed as a rectangle, having a first flow channel structured on a surface thereof, four first fuel input holes located respectively to four corners thereof, and a first fuel output hole located at a center thereof; a cathode plate, shaped as a rectangle, having a second flow channel structured on a surface thereof, four second fuel input holes located at respective corners thereof, a second fuel output hole located at a center thereof, a plurality of second air input grooves disposed along a lateral side thereof, and a plurality of second air output grooves disposed along another lateral side thereof opposing to the lateral side, wherein the second air input grooves, the second air output grooves and the second flow channel are all communicative in space; a cell unit, shaped as a rectangle, having four third fuel input holes located at respective corners thereof, a third fuel output hole located at a center thereof, a cathode layer disposed at one side thereof to face the second flow channel, an anode layer disposed at another side thereof opposing to the side to face the first flow channel, wherein the four first fuel input holes, the four second fuel input holes and the four third fuel input holes are aligned respectively in positions, wherein the first fuel output hole, the second fuel output hole and the third fuel output hole are aligned respectively in positions; an anode metal net, located between the anode plate and the cell unit; a cathode metal net, located between the cathode plate and the cell unit; at least one anode sealing material, disposed between the anode plate and the cell unit to surround the first fuel input holes, the first fuel output hole, the first flow channel, the cell unit and the anode metal net; and at least one cathode sealing material, disposed between the cathode plate and the cell unit to surround the second fuel input holes, the second fuel output hole, the second flow channel, the cell unit and the cathode metal net.