The latest edition of ‘Technical code for building slope engineering (GB 50330-2013)’ employs a novel seismic active earth pressure formula of retaining wall. However, there exists a certain degree of deviation when seismic earth pressure is calculated by using the formula in the code, and the height of action point of seismic earth pressure has not been given. Based on research results in the literature, we develop a complete derivation of the formula and the action point height of seismic earth pressure, and point out the mistake existed in the code (GB 50330-2013). The transformation method with a rotating computational model of retaining wall is adopted in the formula derivation, in which the seismic active earth pressure computing problem is converted into non-seismic active one. Therefore, the active earth pressure formula for non-seismic condition is developed by applying mechanically derivation process of the active earth pressure. The earth pressure calculating parameters are utilized by rotating earthquake angle. This achievement simplifies the complex solution procedure for the active earth pressure.