A method for controlling directory capacities with an accuracy tolerant ratio includes the steps of: applying for a capacity; linking to a directory; checking whether a remaining capacity is greater than or equal to the applied capacity; updating an occupied capacity of the directory if the remaining capacity is greater than or equal to the applied capacity; checking whether the occupied capacity is greater than an accuracy tolerance of difference between a report capacity and an allocated capacity; updating the report capacity of the directory if the occupied capacity is greater than the accuracy tolerance; checking whether the directory is the top directory; linking to an upper directory if the directory is not the top directory; and updating the allocated capacity of the upper directory. A related system is also disclosed.