As the Earned Income Tax Credit(EITC) massively expanded in 2019, 20% of total households benefit from the credit. Due to this large reform, we expect that any future reform will also largely affect the aggregate economy; thus, the heterogeneous agent life cycle dynamic stochastic general equilibrium (HA-LC-DSGE) model will be widely used in future research. This paper reviews the EITC reforms in Korea since the first implementation and surveys the previous studies, examining the labor supply effects. We address why the HA-LC-DSGE model is necessary to examine the current EITC system in Korea. Then, we provide an example of the HA-LC-DSGE model with a policy simulation of the EITC expansion and explain the model's salient ingredients to understand the results.