To select inbred lines of sweet corn（Zea mays L. saccharata Sturt）as testers by means of North Carolina DesignⅡ（NCⅡ）, 9 inbred lines of sweet corn as testers, 10 new inbred lines of sweet corn as tested lines have been studied.The results indicate that GCA effect for grain yield of inbred lines can be tested accurately by one selected tester and at least 3 testers are needed when not selecting. It’s practical to use inbred lines beyond 3 as testers to estimate GCA effect for grain yield of inbred lines. Evaluating effectiveness of 8 agronomic characctcteristics of testers, plant height, ear length, ear weight, ear diameter, kernels per row. 1000 kernels weight, and growth stages for testers selecting are not strict except bare tip length, cob diameter and kernel percent.