Recently, a method known as pipeline stage unification (PSU) has been proposed to alleviate the increasing energy consumption problem in modern microprocessors. PSU achieves a high energy efficiency by employing a changeable pipeline depth and its working scheme is eligible for a fine control method. In this paper, we propose a dynamic method to study fine-grained program interval behaviors based on some easy-to-get runtime processor metrics. Using this method to determine the proper PSU configurations during the program execution, we are able to achieve an averaged 13.5% energy- delay-product (EDP) reduction for SPEC CPU2000 integer benchmarks, compared to the baseline processor. This value is only 0.14% larger than the theoretically idealized controlling. Our hardware synthesis result indicates that the proposed method can largely decrease the hardware overhead in both area and delay costs, as compared to a previous program study method which is based on working set signatures.