Grafting of long-chain branched (LCB) on the backbone of polybutene-1 (PB-1) with its good properties is an effective approach to achieve high melt strength (HMS) PB-1 for replacing with low softness HMS-PP. The aim of this investigation was to analyze the influence of different amount of trimethylolpropane trimethacrylate (TMPTMA) during the irradiation process in production of LCB. Structural modification of PB-1 and the presence of Long-chain branched was successfully confirmed by measuring the rheological properties in shear and extensional mode. Disappearances of the Newtonian-plateau, shifting of onset of shear thinning to lower frequencies, increase of storage modulus (G′) in terminal region, and rise of the relaxation time in all gel free irradiated samples approved the presence of LCB structure. All of the samples also show the pronounced strain-hardening behaviors. Higher LCB content achieved with increase of the TMPTMA content in lower irradiation dose. Increase of irradiation dose and TMPTMA content in PB-1 simultaneously caused to increase of gel content because of the crosslinking reaction