Abstract: The hydrophobic tetrahydrofuran solution of PVC was introduced onto a specially shaped filter paper with the help of a mould to fabricate a barrier ring, in which 1 μL of a reagent solution, containing HgSCN and Fe(NO3)3, was added to form a detection zone, thus forming a selective S2--ion detector with definite size and shape. The volume of sample introduction was set at 10 μL. When the sample solution comes in contact with the barrier ring, only S2- ion can osmosed through the barrier into the detection zone, and reacts with HgSCN to form HgS and liberates SCN- ion quantitatively, which in turn reacts with Fe3+ ion to form a red colored complex, the intensity of which is transformed into digital signal and pixel density by the scanner and software of the computer in succession. It was found that linearity range for S2- was kept between 65 to 2 000 μmol·L-1, and detection limit (3S/N) found was 36 μmol·L-1. The detector was used in analysis of samples of river water and sludge, values of S2- content found were in consistency with the results obtained by the method of GB standard.