Fiber lasers have huge advantages compared with the traditional lasers.This paper proposes a novel all-solid squarelattice Yb3+-doped Photonic Crystal Fiber（PCF）for the development of fiber lasers with still better output characteristics and simulates its structure and properties by using the Finite Element Method（FEM）.By designing defect positions and optimizing the sizes of B2O3-doped rods

it enables the Mode Field Area（MFA）of the fundamental mode of this fiber to reach 4 405μm2 at 1.06μm and satisfy the conditions for single-mode transmissions and low bending loss properties at the same time

i.e.maintaining single-mode transmissions when the bending radius is larger than 8cm.This PCF can be used as a gain fiber in high power fiber lasers.