An anticipated transient without scram induced by main steam isolation valve closure (AMSIV) could subject a nuclear power plant to the most severe of accident conditions. The Chinshan plant analyzer contains a complete boiling water reactor system model and can be revised easily for the user’s purpose. These features make the Chinshan plant analyzer suitable for AMSIV analysis. The capability of the Chinshan plant analyzer to analyze an AMSIV is illustrated. An AMSIV is simulated, and the simulation results are similar to the results of other research. Furthermore, the AMSIV response of reducing reactor power by decreasing reactor coolant inventory is simulated, and the results of the simulation are similar to those of other research. During this transient, the reactor power is decreased. However, the margin to core uncovery is also decreased. In addition, a method of reducing the reactor power by increasing the feedwater temperature is studied. The mechanism of reducing the reactor power is associated with decreasing the inlet subcooling. Sensitivities of key parameters are also analyzed. A large negative void coefficient causes an undesirable large peak in the reactor power. A small recirculation pump moment of inertia decreases the reactor power.