A maize fiber processing system for extracting maize starch, the system comprises: a pressure curved screen group, a fiber washing sink group, an enzyme preparation adding device and an external enzyme reaction tank, wherein, the pressure curved screen group has multiple stages of pressure curved screens, the pressure curved screens are used for separating fiber slurry containing starch and protein into screen overflow and screen underflow, each stage of the pressure curved screen has a fiber slurry inlet, a screen overflow outlet and a screen underflow outlet; the fiber washing sink group is used for providing a place for washing the fiber slurry by washing water, the fiber washing sink group has multiple stages of fiber washing sinks, each stage of the fiber washing sink has a screen overflow feeding port, a screen underflow feeding port and a discharge port; the enzyme preparation adding device is used for adding enzyme preparation into the maize fiber processing system; and the external enzyme reaction tank is connected to a discharge port of a middle stage of fiber washing sink, the external enzyme reaction tank is used for receiving the fiber slurry in the middle stage of fiber washing sink and providing a place for enzyme reaction, the fiber slurry is returned back to the fiber slurry inlet of a next stage of pressure curved screen posterior to the middle stage of pressure curved screen through a returning pipe after predetermined time, characterized in that, the screen underflow contains screen underflow washing water, a screen underflow washing water dividing pipe is provided in a second stage of pressure curved screen posterior to the middle stage of pressure curved screen, the screen underflow washing water dividing pipe is used for dividing part of the screen underflow washing water, so as to control dry substance concentration in the external enzyme reaction tank, the remaining screen underflow washing water is transported to the screen underflow feeding port of the middle stage of fiber washing sink, and the divided screen underflow washing water flows back into the maize fiber processing system by the screen underflow washing water dividing pipe. the pressure curved screen group has multiple stages of pressure curved screens, the pressure curved screens are used for separating fiber slurry containing starch and protein into screen overflow and screen underflow, each stage of the pressure curved screen has a fiber slurry inlet, a screen overflow outlet and a screen underflow outlet; the fiber washing sink group is used for providing a place for washing the fiber slurry by washing water, the fiber washing sink group has multiple stages of fiber washing sinks, each stage of the fiber washing sink has a screen overflow feeding port, a screen underflow feeding port and a discharge port; the enzyme preparation adding device is used for adding enzyme preparation into the maize fiber processing system; and the external enzyme reaction tank is connected to a discharge port of a middle stage of fiber washing sink, the external enzyme reaction tank is used for receiving the fiber slurry in the middle stage of fiber washing sink and providing a place for enzyme reaction, the fiber slurry is returned back to the fiber slurry inlet of a next stage of pressure curved screen posterior to the middle stage of pressure curved screen through a returning pipe after predetermined time, characterized in that, the screen underflow contains screen underflow washing water, a screen underflow washing water dividing pipe is provided in a second stage of pressure curved screen posterior to the middle stage of pressure curved screen, the screen underflow washing water dividing pipe is used for dividing part of the screen underflow washing water, so as to control dry substance concentration in the external enzyme reaction tank, the remaining screen underflow washing water is transported to the screen underflow feeding port of the middle stage of fiber washing sink, and the divided screen underflow washing water flows back into the maize fiber processing system by the screen underflow washing water dividing pipe.