Recently, the study on the multifractal nature of Internet traffic has been becoming a hot-point in the field of study on communication networks. There have been some results on the problem of the source ofmultifractal in Internet traffic, most of which think that the source comes from the hierarchical feature of networks protocols. However, these results ignore the fact that the traffic load in modern Internet is very heavy, which makes important effects on traffics. After analyzing the existing results, it is found that,in the case of heavy loading,the source of the multifactal in Internet traffic is the aggregation of lots of TCP(transmission control protocol)connections,as well as the particular sending behavior of TCP protocol.To support the find,means of wavelet analysis,simulation,and practical data calculating are used.As the find is concluded on the base of practical case in Moden Internet,it is more approach to the truth than existing results,and is more valuable in neworking designing and performance evaluating.