Currently，in the experiment of measuring the surface tension coefficient of liquid with pull-off method， when the liquid film breaks，the judge of the moment could cause artificial error. In this paper，a set of experimental equipment which can measure the tension in high frequency is built by using the PASCO experimental platform. With this equipment，the tension acting on the metal ring is measured systematically. The process of the metal ring getting out of water is studied. The change of the interracial tension and the buoyancy in this process are also analyzed. The surface tension coefficient of water in air is extract through fitting the data measured. The coefficient achieved in this paper is 0.0705 N /m which had about 2.7% difference from the standard value.