Rubidium isotope analysis has important application value in geological exploration and environmental detection. Based on tunable laser atom absorption spectroscopy technology combined with thermal decomposition of the sample, a rubidium isotope absorption spectroscopy measurement device is bulit to realize rubidium isotope ratio stability detection. And the atomic generator is designed by a new micro-channel array structure, which enhances atomic beam collimation capability, effectively suppresses the doppler effect of the spectrum and improves the resolution of rubidium isotope absorption spectrum. The device adopts tantalum metal to make the atomic generator with a diameter of 6 mm, and the micro-channel array with a diameter of 1 mm is stacked inside the atomic generator which can be heated resistively to 3000 ℃. In this experiment, the rubidium carbonate sample is catalyzed to release rubidium atom beam at high temperature (600 ℃), while a probe laser is used to obtain high resolution rubidium absorption spectrum. The rubidium isotope ratio (⁸⁵Rb: ⁸⁷Rb) of natural abundance rubidium carbonate samples is 2.441±0.02 by combining the inversion of the spectral line parameters, the detection error is 4.8%, and the detection limit of ⁸⁷Rb is 1.76‰ (3σ). The experimental results show that the multi-microchannel structure reduces the linewidth of rubidum atoms by 450 MHz (half height full width) compared to the single-channel structure, which can effectively distinguish the absorption characteristics of rubidium isotopes. The device has a high detection accuracy and a high spectral resolution, allowing for a possibility for the measurement of metal isotope abundance analysis, which has a broad application prospect.