In this study, using a nonlinear-polarization-rotation (NPR) mode-locked fiber laser with positive dispersion as a testbed, the polarization characteristics of the pulse are analyzed in both complete mode-locked and composite mode-locked states. The switching from dissipative soliton (DS) and noise like pulse (NLP) can be achieved by making simple modifications to the polarization controllers (PCs). Under a fixed pump power, only adjusting the PCs can obtain a composite mode-locked state caused by the spontaneous switching of pulse states. By comparing and analyzing the polarization characteristics of the pulses in the two mode-locked states, it is observed that the synchronization of the longitudinal modes corresponds to the complete synchronization of the orthogonal polarization components. Whereas, the composite mode-locked of the longitudinal modes in partial synchronization corresponds to the partial synchronization of the orthogonal polarization components. It is proved experimentally that the orthogonal polarization component controls the synchronization between the longitudinal modes. This work is of significant importance to understanding the emergence of complex dynamics in mode-locked lasers and developing stable laser dynamics technology.