The design principle and experiment result of a novel kind of wide-band shaping parabolic mirror for high power laser processing are introduced. According to the geometrical optics, the focusing spot of this parabolic mirror is studied by ray tracking. It is demonstrated that after being focused by this parabolic mirror, the original circular laser beam could be shaped into the narrow strip with uniform distribution of light intensity. The laser hardening is carried out for 45# steel using crosscurrent CO2 laser and the parabolic mirror, the laser hardening band size and hardened depth are tested, then the hardened layer shape and microstructure in the hardened layer are observed and analyzed. The results show that the micro hardness is 3.5～4 times as high as the unquenched area which reaches 540～580 HV0.3, when the laser output power is 3 kW, the length of the strip spot is 12 mm and the scanning speed is 15 mm/s . The hardened depth is approximately 1 mm, the single quenching width is larger than 10 mm , and the hardened layer is well-distributed.