1. A computer implemented method for estimating manufacturing target bias for products in manufacturing tools, comprising the steps of: establishing a first data set according to manufacturing target bias history for the products based on a correlation with tools used, wherein the manufacturing tools comprise a first manufacturing tool and other manufacturing tools based on like manufacturing conditions; executing a testing operation for a predicted product in the first manufacturing tool to obtain a first predicted manufacturing target bias; and calculating manufacturing target bias of the predicted product in the other manufacturing tools according to the first data set and the first predicted manufacturing target bias.