Abstract: All parameters are treated as definite numbers in deterministic computation, thus the result sometimes is inconsistent with the practical condition. Base on the character of geotechnical parameters, the uncertainty of the parameters is expressed by uncertainty rational number, and the theory of uncertainty mathematics is induced in the deterministic computation in order to avoid the shortage in the traditional methods. The uncertainty rational number is applied in the sliding computation of retaining wall, and the safe factor is calculated by certainty method and uncertainty method. The comparison of results indicates that uncertainty rational number can consider the uncertainty better of computation parameters, and the result is more detailed and reliable compared with routine methods, so it can be popularized to other fields.