As multimodal communication develops by leaps and bounds, children's multimodal act has increasingly attracted attention, which makes understanding systematically multimodal act of children become essential. This quantitative study analyzes the multimodal characteristics of Chinese children's acts of denial through observing 110 cases of multimodal denial acts of a Mandarin-speaking boy as a case study from the perspective of Multimodal Discourse Analysis. As is shown, compared with verbal denial and non-verbal denial, multimodal denial employed by the target boy occupies the largest proportion of 74.5%, and the most common inter-semiotic relationship is equivalence, accounting for 66%, rather than complementary or supplementary interaction. What's more, the frequencies of the target boy's denial toward the three groups of interlocutors, that is, the elders, the peers and the non-relatives, are different, and denial against the elders as the most common includes 61 cases making up 55.4%, among which the frequency of denial toward the mother takes the first position. By figuring out the characteristics of multimodal denial of the target boy and drawing corresponding implications, this paper endeavors to provide some instructive suggestions to parenting. In daily communication with children, parents need to pay enough attention to children's multimodal acts and react accordingly and properly with both verbal and non-verbal sources so as to create an efficient communication, which are conducive to some positive parent-child education and interaction.