Branched poly(N-isopropylacrylamide)(PNIPAM) endcapped with different azobenzene structures were synthesized via atom transfer radical polymerization (ATRP) using three different initiators (AZO-Br, CH₃O-AZO-Br and HOOC-AZO-Br), N,N′-methylene bisacrylamide (MBA) as branching monomer, and CuCl/tris［2-(dimethylamino)ethyl］amine (Me₆TREN) as catalyst. The effects of UV irradiation on the lower critical solution temperature (LCST) of polymers were studied through dynamic light scattering (DLS), which reveals the self-assembly behavior of branched PNIPAM in aqueous solution. The results show that the azobenzene structure affects the LCST of PNIPAM after UV irradiation, the LCST of AZO-PNIPAM is a constant (27 ℃), the LCST of PNIPAM-AZO-COOH increases 1 ℃ (30.5 ℃～31.5 ℃) and the LCST of CH₃O-AZO-PNIPAM decreases 1 ℃ (25.5 ℃～24.5 ℃) during UV irradiation, the three polymers represent different self-assembly behavior.