Nested variance has been widely used in evaluating the quality of geological data. In fact, its computing process is complex, especially in the work with many samples such as the  geochemical exploration and the manufacturing of the standard sample. As no software now can compute nested variance directly, people usually use the counter to count it or compute the F value in Excel so as to get the critical value through checking the table. Aimed at solving this problem, this paper has compiled the program in VBA language in Excel with the purpose of realizing the computation of threeclass nested variance convincingly. At the same time, this paper discusses the utilization of the t-test in twin-swatch which collects samples two times but tests every sample only once.