Structural Stability is always complex problems in structural design. Select an appropriate safety factor considering the logical failure probability based on the importance and project economics is a statistical issue and related to the engineering judgments. Safety factor that definition in regulations, relies more on experience and engineering judgments and laboratory work, that for various reasons for most same type of element are defined the same. Members buckling problem with variable section is very difficult find accurate solutions to it. In this paper using the subset simulation which is a very fast and efficient compared with the conventional Monte Carlo simulation method, the probability of failure of a common element with linear change in cross-section will be discussed in three different cases. Accordingly, effect of each the affecting parameters on buckling of column with variable section on the probability of failure was investigated in MATLAB software. The analysis results showed that the sensitivity of the calculated failure probability in such member to the amount of coefficient of variations of length and modulus of elasticity of the column.