Abstract: Based on empirical genetic-simplex algorithm(EGSA),an analytical method of the interior stability of soil-nailed structure for deep foundation pits was proposed.Compared with genetic algorithm(GA),it was shown that EGSA was better than GA.The calculation of the integral stability of a practical engineering example was carried out by using the proposed method and commercial software respectively.It was shown that the most dangerous sliding-plane could not be found out and its evaluation on stability was unsafe by using the commercial software.Furthermore,during calculating the interior stability of soil-nailed structure,the soil deposit was commonly regarded as homogeneous.In this paper,the stratified character of soil deposit was considered.