Abstract: The fast, accurate and highly automatic power regulation ability in a large range is a main research objective of advanced nuclear power plant control strategy. In the current PWR plant, the mechanical shim control and operation strategy is a good method that could meet all above requirements. In mechanical shim, control rods are mainly used to control core operation. Thus the rod worth has a great influence on operation ability. This paper has studied the influence of increased gray control rod worth on operation ability. The results show that increased gray control rod worth and improvement of rod worth axial distribution could enhance load follow operation ability obviously. The analysis results of this paper have a great reference meaning to the design improvement of rod cluster control assembly and the research on advanced PWR nuclear power plant control strategy.