To provide a fault simulation method by which processing time can be shortened.

The fault simulation method includes at least a step of calculating code coverage of test patterns to functional blocks, a step of preparing a list indicating relation among the test patterns, the functional blocks, and their internal nodes, and a step of preparing fault assuming information which assumes faults only for the functional blocks for which RTL codes are executed and their internal nodes. The method also includes at least a step of executing fault simulation for a test pattern on fault-assumed nodes for which the faults are assumed in the order of the code coverage, a step of preparing fault dictionaries on which fault-detected codes from which the faults are detected and a fault recognition rate of the test pattern are described, and a step of removing the overlapping fault-detected nodes from the fault-assumed nodes of the test pattern on which the fault simulation is not executed. In addition, the method also includes at least a step of calculating the total fault recognition rate by combining the fault dictionaries.