Accumulated intensity noises are investigated and the noises are induced by cross-phase modulation (XPM) effect and amplified spontaneous emission (ASE) in dynamic intensity-modulation direct-detection (IM-DD) optical fiber links with multiple fiber segments. A reasonable correction for Q parameter while computing the transmission penalty considering higher order XPM effect is added in the expression of XPM induced degradation. The effect on bit error rate of dynamic lightpath link caused by the two noises is elicited through simulation analysis. The relation between XPM effect and the links’ structure parameters in dynamic network, including the length of fiber segments, wavelength spacing, amplified spontaneous emission noise from amplifiers, etc., are proposed theoretically and numerically, and it is very useful for dynamical link establishment.