We calculate the 0($\alpha_s$) diagrams for pp $\rightarrow\mu+\mu$ - X in QCD perturbation theory. We find that infrared singularities are wholly cancelled out. And we find that the mass singularities can be consistently absorbed into the quark distribution functions. Using the modified quark distrubution functions, the cross section is given by the form of Drell-Yan model plus some finite terms which are negative and rather small for initial gluon graphs but positive and of the same order with the Drell-Yan term for the final - and virtualgluon graphs.