A method for searching an optimum value of a memory includes the following steps. A first and a second phase delay values of the memory are sequentially set to a plurality of first values and a plurality of second values respectively. amounts of combinations of the first values combining with the second values passing a reading and writing test is recorded. A portion of the first values that the amounts of the corresponding combinations passing the reading and writing test is greater than a threshold is selected. A first value near a median of the selected first values is selected as a first optimum value for setting the first phase delay value. A portion of second values passing the reading and writing test is recorded. A second value near a median of the recording second values is selected as a second optimum value for setting the second phase delay value.