Cadmium is a heavy metal pollutant in environment with high toxicity that severely threats human health. A simple and sensitive method for rapid detection of cadmium ions in water sample is of significant importance. In this paper, a colorimetric method based on aptamer-functionalized gold nanoparticles (AuNPs) for specific recognition were proposed to realize Cd2+ detection. AuNPs aggregate in high-salt solutions because of the shielding of salt to electrostatic repulsion among AuNPs, while aptamers can strengthen the stability of AuNPs and avoid the aggregation. After adding Cd2+ ions, the specific interaction between aptamers and Cd2+ leads to a decrease of free aptamers, which weakens the stability of the AuNPs and results in the color change of the solution. The colorimetric change can be rapidly captured and analyzed by a self-developed smartphone-based colorimetric system (SBCS) within 10 min, which implements the quantitative detection of Cd2+. The results show that Cd2+ ions can be detected with high selectivity and sensitivity with a linear range of 2-20 μg/L and a detection limit of 1.12 μg/L. Compared with other methods, the proposed approach features high sensitivity, high simplicity, easy implementation and high throughout, which provides a promising means for in-situ determination of Cd2+ in practical applications.