We report on the vector nature of rectangular pulse operating in dissipative soliton resonance (DSR) region in a passively mode-locked fiber laser. Apart from the typical signatures of DSR, the rectangular pulse trapping of two polarization components centered at different wavelengths was observed and they propagated as a group-velocity locked vector soliton. Moreover, the polarization resolved soliton spectra show different spectral distributions. The observed results will enhance the understanding of fundamental physics of DSR phenomenon.