Two photocrosslinkable NLO polymers of poly(glycidyl methacrylate) substituted with 4-nitro-4＇-hydroxyl stilbene (PGMAS) and acryloyl-functionalized epoxy-based polymer (PENAA) carrying 4-nitroanline moieties were synthesized and characterized. By using the sulfonium salt cationic photoinitiator BDS . 2PF(6) which can induce cationic or/and radical polymerization, the photocrosslinking of PGMAS and the interpenetrating polymer network (IPN) formed by the photocrosslinking of PGMAS and PENAA simultaneously were reported. The poled and photocrosslinked polymer films and IPN films exhibit relatively stable second-order nonlinear optical activity. The influence of stilbene isomerization in PGMAS films with different crosslink densities on the SHG stability was also investigated.