Ground fissuring in Azar Oil Field (AOF) in Ilam Province that almost happening after heavy rainfalls, has been threatening engineering structures like refinery facilities, oil and gas pipelines, oil well cellars, and some access roads. From the geological point of view, AOF is located on the north limb of the Changoleh anticline, composed of the Lahbari section of the Aghajari geological Formation. Sandstone, siltstone, and claystone are the main rock units in the studied area. Sandstone and siltstones are very loose materials with collapsibility potential. Ground fissures are regularly created almost perpendicular to the anticline axis. In this article, in order to evaluate ground deformation mechanism and related ground fissuring, engineering geological investigation has been used in a company with Radar interferometry technics. Radar interferometry studies using time series analysis based on PS-InSAR technics on two data sets using the Sentinel-1A dataset including 68 images from 2014 to 2020 show that ground deformation in the Azar oil field occurs with two different patterns. Linear and permanent deformation in the northwest of the Changoleh anticline which is in direction with anticline axis and plunging. The other deformation that occurs in the southeast of Changoleh anticline is a nonlinear and periodic deformation with intervals of 5 to 6 years. This deformation occurs with heavy rainfalls in the region. This research reveals that ground fissures in AOF are a consequence of ground deformation related to the enlargement of the Changoleh anticline and collapsing of loose sandstones of the Aghajari Formation.