Abstract: In the situation of a deep excavation adjacent to an existing building, the soil between the retaining wall and the existing basement is limited. Active earth pressure in this case cannot be exactly calculated by using classical Rankine or Coulomb theory. Because of the assumption that sliding soil is rigid and that wall-soil interface is smooth, the methods proposed in current literatures cannot reflect the real mechanism. In this paper, a complete mechanical analysis of the limited soil is conducted, which has considered the lateral and tangential forces between the limited soil and the wall. Then the equations for calculating the active earth pressure are established, and a simplified formula for this case is presented finally. Compared with finite element analysis results, it is found that this formula can give more accurate results than those of previous methods. Meanwhile, it can deal with situations that the strength reduction factor differs in a wall-soil interface. The simplified formula derived has a relatively simple form and a high precision, which make it possible for engineers to get preliminary results of earth pressure under such conditions conveniently.