A program verification method for a nonvolatile memory device includes performing a first failure bit counting operation about a first stage to generate a first failure bit accumulated value and comparing the first failure bit accumulated value and a first failure reference value to determine a program failure. When the first failure bit accumulated value is less than the first failure reference value, a second failure bit counting operation for a second stage is performed to generate a second failure bit accumulated value. The second failure bit accumulated value is compared to a second reference value to determine a program failure. The second failure reference value is different from the first failure reference value.