<p>Stretchable polymer semiconductor film (SPSF) is the core to fabricate the flexible optoelectronic devices, due to its excellent strain-tolerance capacity. Softness of polymer chain realized via introducing flexible segment at the backbone and side-substituents is the effective strategy to obtain SPSFs, but easily causing the relatively instable film morphology and weak energy dissipation ability. Herein, we proposed a convenient side-chain cross-linked strategy to prepare the stretchable SPSF with an outstanding morphological stability for flexible polymer light-emitting diodes (PLED). Styrene group is introduced as ended cross-linking unit into the side chain of fluorene to prepare the intrinsically stretchable alter-copolymers semiconductors poly(9, 9-diphenyl-4-((6-(4-vinylphenoxy)hexyl)oxy)-9H-fluorene)-alt-(1,8-bis(4-phenoxy)octane) (PCm-<i>alt</i>-C8). Interestingly, PCm-<i>alt</i>-C8 cross-linked film easily obtained via thermal treatment at 180 °C, had stable morphology, excellent solvent resistance and deep-blue emission simultaneously. Compared to the controlled PEt-<i>alt</i>-C8, PCm-<i>alt</i>-C8 cross-linked films also present an excellent strain-tolerance capacity with larger crack initiation strain rates and the elongation at break (both enhanced by about 90%). More important, stretchable PCm-<i>alt</i>-C8 cross-linked films showed a stable electroluminescent and electrical property with large stretching degree (&gt;30%) and hundreds of cycles of cycling stretch deformations, suggesting their excellent strain-tolerance capacity. Therefore, side-chain cross-linking is a universal strategy for the preparation of high-performance SPSF in flexible optoelectronics.</p>