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The evolution and formation mechanism of surface nanorelief associated with martensitic twin colony (MTC) in Mn-based alloy are studied by use of the phase-field finite element method. The calculation results show that the maximum height of nanorelief is about 30 nm and the maximum nanorelief angle is about 3.2°. The MTC can form during the microstructure evolution. The nanorelief in the same MTC or in different MTCs with the same orientation may have the similar features, which is different from that in the adjacent MTC. The top and bottom edges of one nanorelief correspond to different martensite twin boundaries (MTBs). A bigger stress and a higher plastic deformation distribute around MTC interface than MTB, and the interfacial migration of MTC is greater than MTB. The grain orientation and external stress directly affect the nanorelief and MTC. The biclinic nanorelief (tent-shape and V-shape) evolves from the monoclinic nanorelief. The surface relief angle of MTC is proposed to classify the nanorelief angles and the sum of relief angels (θ1 and θ2) for two adjacent MTCs satisfies θ1 + θ2 = 90°. For different MTCs with the same orientation, their surface relief angles equal to each other.