An interesting phenomenon of transient photo-voltage in the InGaAs p-i-n photo-detector induced by pico-second mode-locked lasers illumination was found. The response voltage presents an obvious negative valley after a rapid rising and a slow relaxation trailing. The amplitude of the negative and positive peak voltage increases with the fixed ratio about 20% with the linear characteristic of the photodiode, then the ratio decreases until the negative valley disappears with the pulse energy increasing with the nonlinear characteristic of the photodiode. By establishing the p-i-n equivalent circuit model and solving the RLC oscillation equation, the appearance and disappearance of the phenomenon can be explained by the non-negligible inductance and the increasing junction capacitance.