In this paper, a uniform axial line_focus, which is important for the x_ray lase r amplification pumped by picosecond and femtosecond laser pulses, is generated by a binary_phase Fresnel zone plate. The performances of the plate are tested u sing a ultrashort_pulse laser. The results show that the length and the width of the line_focus are ～5mm and ～100μm respectively, when coupled with a 125mm f ocal length lens. The ratio of the peak intensity at the center of the line focu s to the intensity outside around the line focus is 7:1