Abstract:To explore the reduction color and the sudden of coal- measures characteristics, periodic discontinuity, that is the non- gradual cyclic sedimentation between intermittent and filling phases, as well as the causes obviously distinct from other sedimentary strata. Methods: Applying "present being a key to past" principle. On the one hand, the survival potential of modern plants, the stabilization on surface clastic sediments by the plants, and the macroenvironment effects of plants on water conservation and climate regulation were investigated; On the other hand, the succession process of the occurrence, development, flourishing and withering of plants in the geological time, and the formation and evolution of each coal- forming period on the basis of the research findings (paleontology, strata, coal- measures, coal seams, coal quality, etc )were analyzed. Comparative sedimentology method was used to compare the different functions in each stage of both sides, and a series of evidence chains were deducted.Results: It is deduced that the coal- forming period is the producct of the development of plant succession and renewal to the peak stage when the plants were extremely flourishing with strong colonizing ability and population effect. The large- scale development of plants in each coal- formation period has changed from the passive stage of being vulnerable to the scouring and transformation of rivers, waves, tides and other fluids to actively limiting the lateral erosion, migration and convergence of rivers, and suppressing the heights of waves and tides. It is a process from individual survival to group effect and a traceback process in accordance with law from the modern fragile plants ecology to the strong basin- controlling vegetation system in the coal- forming period.It is a full display of plant functional potential and a qualitative leap. Under the domination of the vegetation in coal- forming period, the accumulation and collapse of terrigenous clastic sediments reservoir control the shrinkage and expansion of basin clastics and the sudden discontinuous sedimentation of coal- measures, leading to the formation of special sedimentary bodies, such as a divergence, thinning and missing of the basin margin, the intermittent deposition of breccia in coal seam, syngenetic multistage banded sandy body, epicontinental sea multiple barrier systems and Yoredale cycles. Conclusions: The study of plant action in coal- forming period has filled in the gaps of coal geology and can reasonably explain some abnormal phenomena in coal geological explorations and researches.