Abstract: In a dynamic multimodal discourse (MDA)， different modal semiotic systems all have meaning potential and three meta-functions—ideational function， interpersonal function and textual function. A dynamic multimodal discourse-maker chooses different elements from transitivity， mood， modality and cohesion in the linguistic mode， from image vector， contact， social distance and attitude in the visual mode and from sound perspective and social distance in the aural mode， and then makes all these elements interact with each other in order to create either complementary or non-complementary intersemiotic relationships. After an intersemiosis of the film Philadelphia， it is proven that the linguistic mode plays a vital role in theme construction， but the visual and aural modes are indispensable and supplementary to it.

Key words: multimodal discourse analysis (MDA), dynamic multimodal discourse, intersemiosis, Philadelphia