we present a theoretical study on a four-level atom system with a triplet ground state and an exicited state driven by two coupling fields, a rf field and a probe field. The absorption spectrum is characterized by two EIT. It can be found that the linewidth of the two EIT change with the relative phase of the two coupling fields. The linewidth reaches the minimum when the relative phase is equal to . It is more easy to modulate the linewidth of EIT by this means.