In this work, a novel and effective ratio fluorescent porphyrin metal-organic framework (MOF) probe by encapsulating UiO-66(OH)2 into the porphyrin MOF (PCN-224) was prepared, showing the excellent fluorescence performance in detecting Cu2+. In this probe, the signal from the green-emission UiO-66(OH)2 encapsulated in PCN-224 was deemed as an effective reference, thus affording an effective built-in correction in complex environmental effects. The red-emission PCN-224 contained the active site for detecting Cu2+. At the same time, Cu2+ can selectively quench the fluorescence intensity of PCN-224. The ratiometric probe therefore gave an effective and reliable Cu2+ determination platform with an LOD value as low as 0.068 nM. This LOD result was better than the Cu2+ concentration limitation in drinking water regulated by World Health Organization (WHO) and reported by some other methods. This provides a simple new sensor for rapidly detecting copper ions, which can be further expanded in various environmental and biological analysis tasks.