Abstract Passive earth pressure against retaining wall depends on a number of factors such as, soil friction angle ϕ, soil wall friction angle δ, backfill angle (ground surface inclination behind wall β, inclination of wall face on horizontal α, and surface of rupture. Several theory have been developed to over come this problem, i. e., determine the coefficient of passive earth pressure using the plane surface of rupture. One of the important parameter which effect on the coefficient of the passive earth pressure surface of rupture. In the present paper , formulation is proposed for calculating coefficient of passive earth pressure on a rigid retaining wall undergoing horizontal translation base on surface of rupture consisting log-spiral and linear segments assisted by computer program (MATLAB program used). The present study is compared with coulomb's results. The comparison between present study and coulomb's values shows the present study predict values of earth pressure much less than those of coulomb's values specially if δ≥ 0.3 ϕ. Those results agree with anthers researches In order facilitate calculation coefficient of passive earth pressure, using the proposed equations, a modified coefficient of passive earth pressure is provided. It is function of (ϕ, δ, β, α).