Abstract: A micro robot fish is presented.Firstly,the swimming movements of subcarangiform,carangiform and rajiform fishes are simplified and abstracted,and flexible bending is considered as a simplified swimming movement of these swimming modes.Secondly,inspired by the muscular hydrostat structure of squid/cuttlefish fin,flexible fin with the function of flexible-bending is developed,which uses elastic mechanism of animals and is actuated by shape memory alloy(SMA) wires.Then thermodynamics analysis of SMA wires is done to optimize the actuation of SMA wires.Finally,a caudal-fins-propelled micro robot fish based on flexible fins is developed,which is controlled remotely,and swimming experiments are also carried out to realize the swimming movement of subcarangiform and carangiform modes.The micro robot fish has no rotational or sliding parts,and can swim quickly,quietly and stealthily.