The linear optical sampling (LOS) technique enables the full-field information acquisition of ultra-high speed optical signals with low bandwidth optoelectronic devices. Compared to conventional coherent detection method, LOS is a more powerful tool to monitor ultra-high speed optical signals, since it gets rid of the bandwidth limitation of electronic bottleneck. In this paper, the LOS is proposed to implement the characterization of bound state solitons generated from a passively mode-locked fiber laser. According to our experimental results, it is confirmed that the LOS enables more accurate measurements with much higher resolution in both time and spectral domains than conventional measurement devices.