The metal circular arc hole array structure consisting of two symmetrical large and small circular arcs, at the positions of up and down, left and right, is proposed. In order to obtain an extraordinary optical transmission phenomenon, we use Fabry-Perot cavity formed by the structure to enhance the coupling of surface plasmon polariton (SPP). At the same time, a refractive index sensing property is investigated based on the phenomenon. The effects of the radiuses of big and small circular arc holes, the center distance of two circular arcs and the array period on extraordinary optical transmission phenomenon are investigated with the utilization of finite-difference time-domain (FDTD) method. It is found that when the radius of the big and small circular arcs are 95 nm and 70 nm, respectively, the center distance of the two circular arcs is 100 nm and the period is 425 nm, this structure has an extraordinary optical transmission phenomenon and its sensitivity is 279 nm/RIU. These results serve as a theory reference for the design of next-generation high-performance micro-nano plasmonics sensors.