The invention discloses a production method of a composite fiber cement board, and belongs to the technical field of building materials. The production method comprises the following steps: mixing microcrystalline cellulose with a sodium hydroxide solution, cooling the obtained solution, adding a precooled urea solution, stirring and mixing the obtained solution, centrifuging the obtained solutionto obtain a microcrystalline cellulose solution, dropwise adding an etherifying agent to the microcrystalline cellulose solution, performing constant-temperature stirring and reacting, cooling the obtained solution, adding urease and a calcium nitrate solution, continuing a reaction, concentrating the obtained reaction solution, drying the concentrated reaction solution to obtain etherified microcrystalline cellulose, performing a constant-temperature and constant-pressure reaction on the etherified microcrystalline cellulose and a sodium methoxide solution, cooling the obtained reaction solution, adding chloromethane, performing a constant-temperature and constant-pressure reaction, carrying out reduced pressure concentrating, drying the obtained concentrate to obtain modified microcrystalline cellulose, mixing cement, the modified microcrystalline cellulose, a water reducer and a defoamer, carrying out injection molding, and curing the molded mixture to obtain the composite fiber cement board. The composite fiber cement board obtained in the invention has excellent mechanical properties.