Relationship between grain size of total suspended solids (TSS) and particulate organic carbon (POC) content is the base of studying POC transportation and flux in river. Based on sedimentation classification, POC in size-fractioned TSS of The Yellow River was studied by multiple linear regression. The results indicate that: with the median diameter increasing, POC is decreased in a logarithm tendency, the maximum is 0.56% lower than the other rivers; POC is different in the same size-fractioned TSS between characteristic sample stations: the estuary > Huayuankou > Lanshou > Tongguan > Lijin, for example POC is 0.661%, 0.627%, 0.550%, 0.505%, 0.493% in TSS of which the grain size is < 8 microm; the proportion of POC in size-fractioned TSS has little distinction, POC is decreased remarkably with the increasing of the grain size of TSS, and more than 80% of POC is concentrated in the particles < 16 microm while over 95% of POC is concentrated in particles of size < 32 microm. So the transportation of POC is consistent, the main control of transportation of POC is attributed to the grain size of TSS.