Microwave plasma chemical vapor deposition (MPCVD) is a promising method for the large-scale production of high-quality graphene. The aim of this work is to investigate the effect of in-situ hydrogen plasma post-treatment on the MPCVD-grown graphene films. By simply varying the duration time of in-situ hydrogen plasma, surface morphology, number of layers and defect density of as-grown graphene films can be manipulated. The role of hydrogen plasma can be proposed from our observations, promoting to further grow graphene films in the early stage and consequently acting as an etching agent to thin graphene films in the later stage. On the basis of above mechanism, monolayer graphene films with low defect density and smooth surface can be grown by adjusting the times of the growing step and the plasma post-treatment step. This additional in-situ hydrogen plasma post-treatment may be significant for growing well-defined graphene films with controllable defects and number of layers. (C) 2016 Elsevier B.V. All rights reserved.