Online estimation of electromechanical oscillation modes using ambient PMU data is adopted for monitoring the China Southern Power Grid (CSG). After some preprocessing steps, the ambient PMU data is processed by ARMA (Autoregressive Moving average) method, different identification results are obtained from multiple PMU sites. Then by utilization of a clustering method, oscillation modes representing the system operating conditions are derived. In this paper, we report on the preliminary results in CSG and restriction on the ambient data usage is explained. Application of ambient data analysis for oscillation event study is also proposed to judge the oscillation type by comparing the estimated damping ratio value before and during ringdown period. Some suggestions on further ambient data analysis study are also discussed.