In the study, five improved maize inbreds were crossed with five testers which are key inbreds of Lvdahonggu group by NC-Ⅱ mating design. The potential utilization of improved lines was evaluated based on the analysis of heterosis and combining ability of ear traits in 60 000 plants per hectare. The resuits showed that inbred lines J1218 had higher general combining ability（GCA） on kernel yield per plant （KYPP）, and it crossed four high yield hybridized combinations, and thus it was a successful improved line. The GCA of KYPP of J1405 and J1207 was lower, but they crossed a high yield combination respectively. Thus, the two lines may be of some value in use. The combination pattern of improved inbred x Lvdahonggu group was in accordance with the heterotic pattern of PAx Lvdahonggu group. It could be used to breed maize variety with high yield and dense planting. In breeding, the PA inbred could be used to improve America germplasm.