In consideration of the drawbacks of mass-spectrometry in isotope analysis, a spectroscopy based on Degenerate Four-wave Mixing (DFWM) was proposed to analyze atomic isotopes and to overcome these limitations, like limited resolution, higher detection limits and complex sample preprocessing. Rubidium (Rb), cesium (Cs) and potassium (K) isotopes were selected as measured samples and an atomizer based on graphite oven was used to atomize these compounds into atomic steams. The analytic results show that the DFWM spectroscopy has a higher resolution and it can distinguish isotopes and hyperfine structures of the three elements clearly. The measured isotope abundance ratio of Rb isotope is (2.649±0.002), which is superior to the sensitivity of traditional mass spectroscopy. The detection limits of proposed method is as low as 5.4 fg/ml, 0.63 pg/mL and 0.09 fg/mL for Rb, Cs and K isotopes,respectively. Obtained results demonstrate that the spectroscopy based on DFWM has a higher resolution, lower detection limit and is more suitable for the isotope analysis as compared with the origional mass spectrometry.