We propose an integrated semantic-pragmatic account predicting the relative reading of necessary conditionals (NCs) (with two typical expression forms: p only if q vs. not-p unless q). It assumes that the reading of NCs is the joint effect of the semantic factor (q being necessary for p is context-independent) and the pragmatic factor (whether q is sufficient for p is context-dependent), and so varies with level of abstraction (abstract vs. concrete materials) in content. Three experiments used equivalence judgment tasks, possibility judgment tasks, and conditional reasoning tasks, respectively, to investigate how expression form and level of abstraction affect the reading of Chinese NCs. Experiment 1 established the equivalence between the two expression forms. Experiment 2 found that response patterns in conditional reasoning about NCs more often indicated the dual interpretation (q is both necessary and sufficient for p) in abstract materials than in concrete ones. Experiment 3 found that patterns of possibility judgments of four cases under NCs more often indicated the dual interpretation in abstract materials than in concrete ones. Overall, abstract NCs more often meant the dual interpretation than concrete NCs did, regardless of expression form. The present findings support the integrated semantic-pragmatic account rather than the mental model theory.