A design, together with a synthesis, has been made of molecular probe SL based on phenamidazole-salicylaldehyde multifunctional molecular probe SL, with its structure confirmed by NMR and IR. These results show that the probe SL is characterized with a fine selectivity and sensitivity performance as for the identification of trivalent metal ions, such as iron(III), chromium(III), aluminum(III) (Fe3+, Cr3+, Al3+), hardly undisturbed by the monovalent and divalent ions. The Job’s Plots method verifies a binding ratio of 1:1 of probe SL to Fe3+ and Al3+ and a binding ratio of 2:3 to Cr3+. The detection limits of Fe3+, Cr3+, and Al3+ are 3.09×10-8 mol/L, 4.82×10-8 mol/L, 2.89×10-8 mol/L, respectively. Then, the detection of the highly toxic Cr3+ by the probe SL has been investigated by fluorescence spectroscopy. It is found that the probe SL has a good selectivity and sensitivity to the Cr3+ ion, proving it to be a Cr3+ fluorescence probe with potential application value.