Abstract: The dependences of laser-induced isotopic discrimination effect on some of laser parameters were studied by the experimental and theoretical methods. This effect mainly stems from the discrepancy of the second-step transition probability between different isotopes. The method by which this effect is lessened or eliminated is given. The isotopic ratios of nature lutetium sample are determined by this method. The experimental results present that the degree of the laser induced isotopic discrimination of lutetium isotope can be lessened by this method.