The invention discloses a reliability determination method and device of a cut-off wall, and belongs to the field of petroleum pipeline protection. The method comprises the steps of according to parameter values of a structural parameter and an externally loaded parameter of the cut-off wall, establishing at least one failure performance function, wherein the at least one failure performance function comprises at least one first failure performance function of which a random variable does not conform to normal distribution; determining a mean and a standard deviation of each first failure performance function, wherein the mean and the standard deviation of the first failure performance function are determined by adopting an equivalent normalization method; according to the mean and the standard deviation of each failure performance function, determining the reliability corresponding to each failure performance function, and obtaining at least one reliability; in at least one reliability, choosing the smallest reliability as the reliability of the cut-off wall. According to the reliability determination method and device of the cut-off wall, the problem that the cut-off wall is low in accuracy is solved, and the effect of improving the accuracy of the reliability of the cut-off wall is achieved. The method and device are used for determining the reliability of the cut-off wall.