This paper is concerned with lag synchronization of two coupled delayed systems with parameter mismatch. Due to parameter mismatch, complete lag synchronization can not be achieved. Therefore, a new lag quasi-synchronization scheme is proposed to ensure that coupled systems are in a state of lag synchronization with an error level. Several simple criteria are derived and the error level is estimated by applying a generalized Halanary inequality and matrix measure. Three examples are given to illustrate the effectiveness of the proposed lag quasi-synchronization scheme. It is shown that as the coupling strength increases, the estimated error level is close to the simulated one, which well supports theoretical results.