Fusion genes, playing a causal role in human tumorigenesis and developments, are deemed as gold standard molecular bi-omarkers in cancer diagnosis, therapy, and prognosis. A rapid, robust and sensitive method detection of fusion gene for point-of-care (POC) diagnosis is urgently needed. Here, taking the advantages of the superior specificity of ligation reaction and highly amplified efficiency of isothermal exponential amplification with pH indicator, we developed a colorimetric method for visual detection of fusion gene with high sensitivity and specificity by the naked eye. More importantly, we first found that fusion gene can be accurately quantified in a wide dynamic range (2 zmol to 2 fmol) by an open-source App with SmartPhone-assisted RGB (Red, Green, and Blue value) reading mode. The proposed method for Visual detection of Fu-sion gene by Ligation-triggered Isothermal Exponential Amplification is termed Vis-Fusion LIEXA. We have demonstrated that the Vis-Fusion LIEXA is a practical and reliable method for accurate quantitative detection of the fusion gene in a complex biological sample at zmol level in 40 min only with a SmartPhone, thereby providing a user-friendly and point-of-care testing (POCT) tool for molecular diagnostics.