Abstract: Mixing of siliciclastic and carbonate sediment is widespread in variable marine sedimentary environments through the Phanerozoic. Terminology of mixing and its classification are introduced in the paper, and the controlling factors upon mixing within systems tracts of depositional sequences are discussed. In general, the punctuated mixing is the most ordinary sedimentation in all systems tracts of mixed depositional sequences, and the source mixing associated with a little facies and punctuated mixing occurs within lowstand systems tract (LST); the facies and punctuated mixing becomes the main sedimentation in the shelf marginal systems tract (SMT) and the late highstand systems tract (HST); and the transgressive systems tract (TST) is characterized by the punctuated mixing with a little facies mixing. It is proposed that the mixing within systems tracts of depositional sequences is chiefly constrained by the patterns of the sea-level changes, i.e., the mixing within LST, SMT and late HST could be induced by amplitude, rate, and time duration of sea-level changes, and the mixing within TST could be related to the source supply. The mixing could be more or less influenced by the former topography and carbonate production in moderate paleoclimate. Fuether more, the regional tectonic activities might be partially responsible for mixing, which means that the cycles of mixing procession within systems tracts of depositional sequences in a sequence set or supersequence could be responses of vpulse regional tectonic activities.