In order to detect and analyze the complex multi-mode dynamics of fiber ring laser (FRL), in this experiment, based on the heterodyne detection method together with radio-frequency spectrum, the output of FRL intensities on two kinds of modulation condition are synchronously detected and analyzed. From the low dimension to high dimension chaos, the total intensity and multi-mode characters can be synchronously acquired. These experimental results show the relationships between real-time intensity and frequency evolution behaviors about single mode and total mode. Moreover, according to experimental results, the chaotic characteristics and inner relationships of erbium- doped fiber ring laser (EDFRL) output mode dynamic can be analyzed.