Large-scale wind turbine generators with power electronic converters that operate near series compensated transmission lines are susceptible to un-damped sub-synchronous oscillations. This sub-synchronous oscillation is called Sub-synchronous Control Interaction (SSCI). With the rapid development of wind power technology, SSCI emerges as a new sub-synchronous oscillation phenomenon. The first SSCI event occurred for a wind farm in America in2009, which resulted in damage to the wind turbines. The origin of SSCI is presented and its characteristics of different types of wind turbines are summarized. Then the research prospect on this field is explored.