Abstract: The paper makes experimental studies on vortex induced vibration of a two degree free vibration cylinder. The cylinder is put horizontally, with the diameter of 5cm and the length of 120cm. The model test could change the frequency of the modeling system vibrating upwards cross and in-line flows by adjusting the number of springs in cross and in-line flows. It has been found the vibrating frequency of the cylinder in in-line flow appears to be "multi-frequency". Under certain vibration frequency and reduced velocity conditions, single-frequency exists in cross flow besides twice-frequency. Consequently, the new trajectories of "egg" and "rain drop" were shown in the tests, different from the traditional trajectories of figure "8" and "new moon", which"" was rarely mentioned in the studies of two degree-of-freedom vortex induced vibration of rigid cylinders with elastic support.