Abstract: For Swift Heavy Ion(SHI) irradiation, at micro-scale, the incident ions are randomly distributed regardless of beam scanning or defocusing. Recently, this nonuniformity of ion irradiation is becoming critical for the cutting-edge applications of SHIs, i.e., fabrication of high-density microporous membranes, and evaluation of single event effect for the aerospace electronics. In this study, a Monte Carlo(MC) code is developed for simulating the planar distribution of incident ions. Statistically, the predicted distributions of latent tracks and micropores show good coincidence with the direct observations of microporous membranes. According to the simulations, the porosities of membranes are predicted as functions of ion fluences and pore sizes. An empirical formula is proposed for the estimation of effective porosity prior to ion irradiation and chemical etching. Moreover, to evaluate the selectivity of microporous membranes, the probability of multi-pores formation is estimated. A balance between the porosity and selectivity of the membranes is suggested. By employing the MC simulations, uniformity issues of ion irradiation at micro-scale are investigated, whose results may serve as important references for single event effect etc.