When the power of the nuclear power plant is increased, it is necessary to supplement the Reactor Coolant System (RCS) with demineralized water through the Chemical and Volume Control System (CVCS). This process is called dilution. The volume control tank (VCT) is an important piece of CVCS equipment with a large volume. Its internal flow and mixing processes are very weak. Therefore, VCT has a strong retention effect on the working fluid in the dilution process. This effect causes the boron concentration of RCS to fail to reach the target value for a long time, thus affecting the safe operation of the nuclear unit. This paper aims to experimentally study the dynamic response of the outlet concentration of VCT during the dilution process. The effects of flow rate, concentration difference, and nozzle diameter on the dynamic response of outlet concentration are studied in the range of 0.17 m2/h to 18.67 m3/h, 2.59 × 102 ppm to 1.05 × 102 ppm, and 0.016 m to 0.049 m, respectively. Detailed outlet concentration–response curves are provided. The experimental correlation for predicting response time is provided. The results show that the duration of the delay stage is negatively correlated with the flow rate and positively correlated with the concentration difference and the nozzle diameter. The response time negatively correlates with the flow rate, concentration difference, and nozzle diameter. The deviation of the experimental correlation is less than 20%. The research results play an essential role in designing and operating VCT.