Fe3O4 nano-particles coated with silica were chemically modified with trimethoxyoctadecylsilane，and then used as the adsorbent for solid phase extraction of silver ion chelated with 5-Br-PADAP in environmental water samples.Coupled with flame atomic absorption spectrometry，a new analytical method for sensitive，rapid and simple determination of trace amount of silver ion in aqueous samples was developed.Effects of some experimental factors such as water sample pH，amount of adsorbent and chelating agent，oscillating time，eluent type and volume，coexisting ions，on the recovery of silver ion were investigated and optimized.The results showed that for 200 mL water sample，the optimal conditions were as follows：sample pH:7.0,adsorbent amount:0.1 g,volume of 5-Br-PADAP solution(0.5 mg/L)：0.6 mL,oscillating time:10 min.The adsorbed silver ion could be completely eluted off by using 6 mL 1.0 mol/L nitric acid.Under the optimized conditions，the detection limit for Ag+ was 0.15 μg/L with an enrichment factor of 31，and the relative standard deviation was 1.4%(10 μg/L，n=6).The proposed method was applied in the analysis of Ag+ in river water，lake water samples with spiked recoveries of 85.0%-94.8%.