Abstract: The application effect of the control rod worth in the criticality extrapolation experiment is studied. The criticality extrapolation experiment is conducted on a zero power reactor, and the analysis is carried out by 2 extrapolation methods, i.e., with and without the consideration of the control rod worth, based on the neutron count rate data. The results indicate that the control rod worth is with great effect on the extrapolation results in the first few extrapolation steps, and the extrapolation 1/2 adding control rod position would exceed the measured critical control rod position without taking consideration of the control rod worth. The extrapolation method taking the control rod worth into consideration is more precise, with better results.