【Objective】 To explore the genetic basis on heading date in rice. 【Method】 Eight single segment substitution lines of Huajingxian 74 were applied as experimental materials to construct seven secondary F₂ populations pyramiding dual QTL, in each of which nine marker genotypes were distinguished to allow estimations of epistatic components for the QTL pairs.【Result and conclusion】 All QTL pairs tested, except for QTL HD3 and HD8, exhibited significantly epistatic effects, accounting for 85.7%. There were 60.7% of 28 epistatic components to be detected with significant estimations at the probability levels of 5% or 1%, where three types of epistatic interactions, e.g. additive-additive, additive-dominance or dominance-additive, and dominance-dominance epistatic effects accounting for 71.3%, 42.8% and 85.6%, respectively. These results further confirmed that the universality and the importance of epistasis existed in genetic systems of quantitative traits, providing useful frames and materials for molecular marker assisted pyramiding breeding on heading date in rice.