The invention provides an online real-time control method for a product manufacturing process and includes: (A) establishing a monitoring equation for estimating a product attribute in view of production line parameters corresponding to respective steps in a manufacturing process of a product; (B) when each of the steps is finished, updating the calculation result according to an online feedback value(s) of the production line parameter(s) corresponding to the finished step; (C) when the updated calculation result in the step (B) indicates that the quality of the product does not meet a required quality specification, adjusting the production line parameter(s) corresponding to the step(s) after the finished step to make the quality of the product meet the required quality specification. According to the method, a key attribute(s) of the display device can be kept within an acceptable specification by adjusting the production line parameter(s) of subsequent step(s).