Fluidelastic instability is one of the main vibration mechanism that cause damage of steam generator tube. Connors relation based on quasi-static fluid forces is widely applied to research fluidelastic instability. In this paper, fluidelastic instability experiments were conducted on rotated triangular tube array subjected to air-water cross-flow. The test section was equipped with 7 row *15 row straight tube bundles. The picth-to-diameter ratio of bundles is 1.48 and the tube diameter is 17.48 mm. Two different frequencies of tube in the lift direction were tested. Critical velocity of fluidelastic instability, damping and hydrodynamic mass of tube bundle were measured in these void fraction of 0, 20%, 40%, 60%, 80% and 90%. Connors relation was fitted according to the data obtained. The results show that, critical velocity increases with the increase of void fraction for tube bundle with the same frequency. Critical velocity varies inversely with natural frequency of tube for the same void fraction. While void fraction is less than 20%, vortex shedding occurs in the tube bundles. With the increase of void fraction, the damping ratio increases first and then decreases. The damping ratio reaches the maximum value at void fraction of 60%. Hydrodynamic mass is inversely proportional to the void fraction. Fluidelastic instability constant K fitted for two different frequencies of tube are both greater than 4.25.