Abstract:Using the improved JC method in association with an example of Hoek2Brown criterion , the variables replacing technique , the compound function method as well as the rational polynomial technique are adopted in the calculation of reliability index to consider the high order nonlinearity and the complexity of the performance func2 tion in geotechnical engineering. Moreover , Monte2Carlo method is employed as comparison. The result s show that the method of adopting the rational polynomial technique is better than the other techniques because it is easier in calculation and more convenient in developing computer program.