The mechanism of high power inter-channel crosstalk attack is analyzed theoretically. The conclusion that power of attack signal and fiber nonlinear refractive index are the main factors causing destructive effect on quality of legitimate signals due to high power inter-channel crosstalk attack is obtained. The effects of high power inter-channel crosstalk attack on quality of legitimate signals and its attack propagation capability are investigated by building a simulation system in VPI software and using the bit error rate (BER) as evaluation index. The results show that high power inter-channel crosstalk leads to quality deterioration of legitimate signals propagated in the same fiber as the attack signal. The higher the power of attack signal is, the closer the channel spacing away from the attack signal is and the greater the fiber nonlinear refractive index is, the more the serious legitimate signals are affected by attack. The high power inter-channel crosstalk has an ability of attack propagation, and attack effect of the attack signal can be propagated to the fourth optical cross-connects (OXC4) when the power of attack signal is 27 dB higher than that of the legitimate signals.