A kind of magnetic field sensor with e ven straight-trenches microstructure is designed based on femtosecond laser mic romachining.The femtosecond laser is used to ablate straight-trenches into cladding of fiber Bragg grating (FBG),and the HF is empl oyed to remove the residual debris and stress concentration in the straight-trenches.Then the magnetostrictive film (TbDyFe) is deposited on the processing region by magnetron sputtering process.When the intensity of external magnetic field changes,it ca n be measured by the change of the central wavelength of the sensor.The microstructure can reduce the fiber cross-sectional area,impro ve the axial retractility of fiber and increase the deposited surface area,so as to improve the sensitivity of sensor probe.The principle of improving the sensor performance by straight-trenches microstructure is analyzed and the fabrication process the and factors affecting sensor performance are described.The magnetic response results of several probes with different parameters are demonstrated.The experi mental results show that processing straight grooves microstructure by femtosecond laser can significantly improve the sensitivity of the sensor probe and the number of straight-trenches is the most significant influence factor.The sensitivity of the probe with m icrostructure can be improved by nearly 4.5times compared with that w ithout microstructure.