A method, for determining constraints related to a target circuit, includes following operations. First circuit speed results of the target circuit under different candidate constraint configurations are accumulated. Breakthrough probability distributions relative to each of the candidate constraint configurations are determined according to the first circuit speed results. First selected constraint configurations are determined from the candidate constraint configurations by sampling the breakthrough probability distributions. A first budget distribution is determined among the first selected constraint configurations. In response to that the first budget distribution is converged, the first selected constraint configurations in the first budget distribution is utilized for implementing the target circuit and generating an updated circuit speed result of the target circuit.