1. A trajectory-based control method comprising: obtaining at least one smoothed coordinate of an object in accordance with an object tracking procedure, wherein the object tracking procedure utilizes a binarized motion skin image and a skin feature image to obtain the at least one smoothed coordinate of the object, wherein the object tracking procedure comprises the steps of: obtaining a possible coordinate of the object in accordance with the binarized motion skin image and the skin feature image; obtaining a prediction coordinate of the object in accordance with the skin feature image and a locked coordinate of the object; obtaining a latest coordinate of the object in accordance with the possible coordinate, the prediction coordinate and an area of the object; obtaining the at least one smoothed coordinate of the object in accordance with the latest coordinate, the locked coordinate and a weighting ratio; and marking the coordinate of at least one non-object in accordance with the at least one smoothed coordinate of the object; performing a function control mode or a cursor control mode in accordance with a first trajectory of the object, wherein the first trajectory of the object is expressed in accordance with the at least one smoothed coordinate; performing at least one system function in accordance with the function control mode; and moving at least one cursor in accordance with the cursor control mode.