Abstract：The smoothing parameters of range split spectrum (RSS) in InSAR ionospheric correction, including multilook numbers and filtering window size, are selected subjectively, so we use international reference ionosphere (IRI) as a reference to evaluate the similarity between RSS and IRI by visual comparison and statistics analysis. Considering the ionospheric distribution, we provide a relatively objective method to select smoothing parameters for RSS. 32×16 (azimuth*range) multilook and 600 pixel size filtering window for two pairs of ALOS-2 PALSAR stripmap data. The ionospheric delay is corrected well. The research shows that the IRI model can be used as a reference to select RSS smoothing parameters in both invisible deformation and slow deformation regions.