Abstract: We present the parton distributions at leading order (LO) coming from GJR, MSTW and CTEQ parton sets and compare them at different momentum scales. Obvious differences exist in their gluon and sea quark distributions at small x region. Itindicates that people have not known the nucleon parton distributions very well. We analysze the influence of higher twist effects, i.e., the shadowing effects and anti-shadowing effects, on parton distributions. Because of the shadowing effects, the twist-4 gluon and sea quark distributions are smaller than the twist-2 distributions at small and middle x region, while, the anti-shadowing effects make the twist-4 gluon and sea quark distributions larger than the twist-2 distributions at x & 2 region. Finally, we present a detailed analysis of how the proton’s momentum is shared among various parton flavors at different Q2 for different parton sets. With the numerical calculation, we show that the MD-DGLAP equations are momentum conservation.

Key words: parton distributions, higher twist effect, evolution equation