Software testing bears a burden of software development, increasing its time and cost. The bugs appearing due to the combination of two factors are well known in the system test phase. The current system testing methods represented by pair-wise tests or orthogonal arrays tests generate test sets by the forms of factors and values. In this study we extract two problems in the system test phase, and propose a solution to solve the problems. The first type of the problems is a survival bugs by the combination of factors among test sets. The second type of the problems is a duplication of factors by extra test case in the test set. We propose a solution which considers combinations of important factors for these two problems.