Today's digital elevation models have many applications in various fields including engineering projects and management of natural resources and etc. One of these applications is a topographic correction in InSAR to find the amount and rate of displacements. The purpose of this paper is to compare the effects of two digital elevation models with a resolution of 30 m and 90 m in order to obtain displacement rates from radar images. Persist Scatterer and Small Baselines methods were used to compute the displacement rate in the region. Processing was performed with both models SRTM and ASTER. The maximum difference between the results from two elevation models is observed in areas with a high elevation difference. In both methods, the number of persist scatterers in the case of model ASTER is less than model SRTM. In areas with low elevation differences, the results of two elevation models are very similar to each other. But in areas with high topography, the low resolution elevation model does not have the ability to deliver results with appropriate accuracy. In PS method there are 0.2 mm difference in maximum and 1.1 mm in minimum of displacement rate field and in Small Baselines method, these rates were 4 and 1 mm respectively. In order to better evaluate the results, six points in the region were examined. The maximum difference between the results was 4 mm. This difference is significant at the ten percent level of confidence. As a result, in areas of high topography, it is necessary to use the more accurate digital elevation model to achieve higher accuracy.