In this study, the method of Zero Extension Lines has been used to evaluate the static and seismic lateral earth pressure on retaining walls. The passive and active lateral earth pressures has been evaluated by assuming plane strain case for the retaining wall. The soil has been also assumed as a homogeneous soil. The earthquake effect has been considered as horizontal and vertical pseudo-static earthquake coefficients. The equilibrium equations along the Zero Extension Lines has been obtained and boundary conditions has been expressed on the earth and along the wall. In order to analyze the retaining wall a MATLAB computer code has been written. The code is capable of static and seismic analyzing the retaining wall in passive and active cases, determining the Zero Extension Lines network and failure zone for the retaining wall, calculating distribution of passive and active earth pressures on the retaining wall and computing the passive and active lateral earth pressure coefficients. The advantage of ZEL method is not requiring the assumption of the failure surface and capability of analyzing the non-associative soils. By using the computer code, the retaining wall has been analyzed in passive and active cases and the ZEL network and failure zone has been determined. Therefore, the values of stress has been obtained in all points of the ZEL network. Then, the lateral earth pressure distribution on the retaining wall has been defined and the passive and active lateral earth pressure coefficients has been obtained. The total lateral force on the retaining wall has been considered as the lateral earth pressure coefficients due to the soil unit weight, surcharge and soil cohesion. The lateral earth pressure coefficients due to the soil unit weight, surcharge and soil cohesion has been presented for associative and non-associative soils. The effect of various parameters on the lateral earth pressure coefficients has been evaluated. Also, the effect of the dilation angle