The main purpose of this paper is to analyze and compare the influence of nozzle size, uneven gravel packing, packer leakage, and dynamic production process on the inflow control effect. First, a new mathematical model of Inflow control devices (ICDs) completed horizontal well is proposed which has two new features. One feature is that the annulus between the sand control screen and the formation is considered. Therefore, the influence of uneven gravel packing can be simulated by adjusting the permeability distribution along the annulus. The other feature is that it accounts for packer leakage by introducing a new parameter named “leakage factor” into the model. Then, the inflow control efficiency is defined and used to quantitatively characterize the inflow control effect, and the influences of nozzle size, uneven gravel packing, packer leakage, and dynamic production process on inflow control efficiency are analyzed. The results show that the nozzle size and packer leakage have the biggest influence on the inflow control efficiency, and the influence of gravel packing is negligible unless the permeability of the packed gravel along the wellbore is extremely heterogeneous.