Based on the seismic，core and slice data，it was found that the main factor for T sandstone reservoir abnormal variation in Colombia M oilfield is dynamic metamorphism caused by thrust fault through analyzing the characteristic of reservoir microscopic structure. The sedimentary environment of T sandstone is littoral-neritic sea，so the reservoir deposited steadily with good properties. Well-5 was drilled through a small thrust fault，of which two sets of T sandstones at the hanging wall and footwall were drilled. Those sandstones drilled are characterized by dense rock cementation，developed fracture，a large number of stylolites found out by microscope，concave and convex contact and stitching between particles，obvious quartz overgrowth and breccias and fracture and inter-granular pore filled with cement. It was analyzed firstly that the dynamic metamorphism resulted from thrust fault caused a local abnormal high pressure zone，in which the quartz grain was crushed and grounded to smaller grain size. Secondly，part quartz was dissolved by pressure solution to become stylolite.Thirdly，the dissolved siliceous cement deposited again and filled residual pore，leading to dense cementation and poor physical property. Combined with tectonic interpretation model and the surrounding well data，the scope of dynamic metamorphism was speculated to be within 15 m. In short，stress concentration is the geological background of dynamic metamorphism，and thrust fault is the direct reason of dynamic metamorphism. Because the range is limited，M oilfield could continue normal development.