Most methods to determine sliding surface of soil nailing wall are based on the assumption that all circular sliding surfaces pass the foot of slope; but the assumption is not always true. In this paper

four kinds of circular sliding surfaces that may appear in reality are summarized and an approach to search the most dangerous sliding surface that does not pass through the foot of slope is put forward using the relationship between the center coordinate and three location parameters of this circular sliding surface. In addition

the calculation formula for the factor of safety of soil nailing wall in Technical specification for retaining and protection of building foundation excavations is discussed and improved. Through comparing and analyzing sliding surfaces and the factors of safety obtained by different methods in three examples

the results show that sliding surfaces and the factors of safety got by the method established in this paper is quite close to those obtained by other methods

so as to verity the feasibility of the method established in this paper. In some cases

sliding surface got by the method established in this paper is very different from traditional method because of the assumption that the all circular sliding surfaces pass the foot of slope. The improved formula which takes the anti-sliding force produced by soil weight along the tangential direction of sliding surface into account can get a slightly greater safety factors under the same sliding surface for other three kinds of sliding surface except for the sliding surface got by traditional method.