A fiber orientation control method comprising the steps of: expressing changes of velocity components of a paper material at an exit of a slice lip by using a mathematical model, wherein the changes of velocity components are caused by manipulating a slice-lip-opening-adjusting means and at least one of an edge flow adjustment means and a side bleed adjustment means of a headbox when supplying the paper material on a wire; setting the mathematical model based on an assumption in which a velocity component in a flow direction of the paper material is proportionally changed in accordance with changes in differences in size of an open of the slice along a cross direction of the slice lip and in which a velocity component orthogonally crossing the flow direction of the paper material is a sum of both changes proportional to an average value of differences of changes in size of an open in a cross direction of the slice lip and changes proportional to changes of at least one of an edge flow and a side bleed of a certain response width from the exit of the slice lip; and conducting a forecasting calculation of changes of a fiber orientation profile in a cross direction by using the mathematical model; wherein the step of conducting the forecasting calculation of changes of the fiber orientation profile in the cross direction by using the mathematical model comprises: calculating a moving average of a moving average of the differences of changes in size of an open in a cross direction of the slice lip, and based on the moving average of the moving average, calculating the velocity component orthogonally crossing the flow direction for the paper material in accordance with the differences of the changes in size of the open in the cross direction of the slice lip. expressing changes of velocity components of a paper material at an exit of a slice lip by using a mathematical model, wherein the changes of velocity components are caused by manipulating a slice-lip-opening-adjusting means and at least one of an edge flow adjustment means and a side bleed adjustment means of a headbox when supplying the paper material on a wire; setting the mathematical model based on an assumption in which a velocity component in a flow direction of the paper material is proportionally changed in accordance with changes in differences in size of an open of the slice along a cross direction of the slice lip and in which a velocity component orthogonally crossing the flow direction of the paper material is a sum of both changes proportional to an average value of differences of changes in size of an open in a cross direction of the slice lip and changes proportional to changes of at least one of an edge flow and a side bleed of a certain response width from the exit of the slice lip; and conducting a forecasting calculation of changes of a fiber orientation profile in a cross direction by using the mathematical model; wherein the step of conducting the forecasting calculation of changes of the fiber orientation profile in the cross direction by using the mathematical model comprises: calculating a moving average of a moving average of the differences of changes in size of an open in a cross direction of the slice lip, and based on the moving average of the moving average, calculating the velocity component orthogonally crossing the flow direction for the paper material in accordance with the differences of the changes in size of the open in the cross direction of the slice lip. calculating a moving average of a moving average of the differences of changes in size of an open in a cross direction of the slice lip, and based on the moving average of the moving average, calculating the velocity component orthogonally crossing the flow direction for the paper material in accordance with the differences of the changes in size of the open in the cross direction of the slice lip.