In the study of the noise characteristics of devices by traditional scattering theory,the incoherent transport and the effect of Coulomb interaction on shot noise are not taken into account, which may not be ignored in real nanoscale devices. Based on the equivalent contact model of the scattering region, we derive a unified scattering theory model for current noise, including the effects mentioned above. Our model covers the whole range of transport regime from coherent transport to incoherent transport. Our model also includes the effects of Pauli exclusion and Coulomb interaction on shot noise. Then, a numerical simulation approach is presented for our model. The approach coincides with the equivalent contact model in the property of the scattering region.