The nonlinear dynamics of a multi-transverse mode 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) under parallel optical injection is experimentally investigated. For a free-running 1550 nm-VCSEL biased at a suitable current, the fundamental and high-order modes can oscillate simultaneously and dominantly operate at the Y Linear Polarizations (Y-LPs). After introducing a Continuous Wave (CW) injection with the polarized direction along Y-LP of the free-running 1 550 nm-VCSEL (named as parallel optical injection), two different scenarios have been investigated experimentally, namely the frequency of injected CW (νinj) is close to the fundamental transverse mode frequency (νfy) (the frequency detuning is defined as Δνf=νinj－νfy) or the high-order transverse mode frequency (νfy) (the frequency detuning is defined as Δνh=νinj－νhy). For the first case, the results show that, during the process of continuously increasing injection power (Pinj), the fundamental mode undergoes diverse dynamical states, but less dynamical states are observed for the high-order mode. With the increase of Pinj, the output power of the high-order mode is decreased gradually. For a strong enough Pinj, the high-order mode can be totally suppressed and therefore the laser operates at single transverse mode, i. e. the mode selection for the fundamental mode achieves. With the increase of Δνf, the minimal injection power required for achieving the fundamental transverse mode selection (Pinj,min) decreases firstly, after reaches a minimum, and then increases. The larger the biased current, the larger the value of Pinj,min. For the second case, during the process of increasing Pinj, both high-order mode and fundamental transverse mode undergo multiple dynamical states. However, the phenomena that the fundamental transverse mode is suppressed has not been observed, i. e. the mode selection for high-order mode cannot be realized.