The UV-Vis absorption and photoluminescence spectral signals of silver colloids and methyl orange (MO) in different pH systems before and after adding Cl- were studied. It was found that the energy transfer efficiency changes with the pH value, i.e., the fluorescence quenching at 428 nm and photoluminescence enhancement at 560 nm was greatly strenthened with the increase of pH of the system. After adding Cl-, dense adsorption layer was formed, leading to stronger spectral signals associated with surface enhancement. On the other hand, because of the decrease of incident light to the inside of Ag-MO complex, energy transfer channel may be suffocated to some extent, the quenching amplitude of 428 nm fluorescence band decreased. Compared with these notable phenomena and discussed with correlative theoretic analysis, it's clear that different molecular structures and adsorption models of MO onto Ag surfaces exist with the changing of pH and the adding of Cl-, which give rise to the different phenomena observed.