By using a genetic model including additive and dominance effects, six important agronomic traits including plant height (PH), number of leaves (LN), length of internodes (IL), length of leaves (LL), width of leaves (LW) and stem girth (SG) in sun-cured tobacco were analyzed for a complete diallel mating design with 8 sun-cured tobacco cultivars or breeding lines and their 28 F1. The results showed that additive effect and dominance effect played important roles in most of agronomic traits in sun-cured tobacco. For 6 agronomic traits, LL and LN were mainly controlled by additive effect, while PH, IL, LW and SG were mainly controlled by dominance effect. The narrow heritabilities of 6 different traits were LL>LN>PH>IL>LW>SG, and the narrow heritabilities for LL and LN were 0.35 and 0.34, respectively, which was relatively high and could be taken in early generations. In addition, the values of additive and dominance effects were estimated and the potential breeding values of different parents and crosses for improvements of different agronomic traits were discussed in respect to predicted values of genetic effects.