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The inherent mechanisms of flow-induced crystallization (FIC), especially the amorphous formation, have been revisited inversely, via in situ swelling small angle neutron scattering (SANS). The neutron contrast between crystalline and amorphous phases of crosslinked high-density polyethylene was strengthened by deuterated o-xylene-d10. Thereby, the morphological evolutions and kinetics of various FIC samples (imposed initial strain: 0.6, 0.9, 1.4, and 2.3) during the swelling process were obtained simultaneously. The half time for swelling to reach equilibrium decreases from ca.39100 s–4500 s for S0.0 to S2.3. Moreover, the evolutions of the expanded long period (LP) are similar to the swelling kinetics. Interestingly, the increment LPt-LP1 increases monotonically from 1.55 nm to 4.32 nm. However, the expanding ratio (LPt/LP1) first increases from 1.05 to 1.13 for S0.0 to S1.4, then decreases to 1.11 for S2.3. Combining ex situ small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) results, current work demonstrates that both crystalline degree and different morphology contribute to the influences of swelling. It suggests that the generated amorphous networks triggered by different strain were endued with various inherent structure and characters, and the nature of amorphous phase can severely affect the swelling behavior.