In the primary circuit of a nuclear reactor, the accumulation of impurities within fuel assemblies can lead to fluid blockages, which, in severe cases, can cause damage to the fuel assemblies, thereby threatening the safe operation of the nuclear power plant. The most critical scenario occurs when the blockage completely obstructs the flow channels, resulting in a lack of cooling in hot spot regions. Currently, research on the simulation of blockage accidents using subchannel models is relatively limited in the public literature. Furthermore, due to the subchannel model's reliance on pressure matrix-based flow field solutions and the impossibility of having a zero cross-sectional area for subchannels, it is challenging to accurately simulate the flow and heat transfer conditions during complete blockage accidents using subchannel codes. This paper presents an improved model for the complete blockage condition, enabling subchannels to effectively simulate such accidents. By analyzing subchannels using experimental results of blockages from public literature, it is found that the improved model can adequately simulate the flow and temperature fields after blockage. This paper introduces a novel approach to simulating blockage accidents, providing a valuable reference for future simulations of blockage accidents in subchannels.