The flat-top beam output is realized through special treatment of the cone area of the optical fiber signal combiner and output fiber and the torsion treatment of the output fiber. The experimental results show that the beam intensity distribution of 4 × 1 signal combiners with a 20/130 μm (the core diameter is 20 μm, the cladding diameter is 130 μm) fiber input and 100/120/360 μm (the core diameter is 100 μm, the cladding diameter is 360 μm, the diameter of the low refractive index layer between the core and cladding is 120 μm) fiber or 200/220/360 μm fiber output is not a flat-top distribution; the strength distribution is relatively scattered. More fiber mode will be excited by twisting the output fiber. Then, a 200/220/360 μm fiber was spliced between the cone area and output fiber. The intensity distribution of 4 × 1 signal combiner is uniform and has a flat-top distribution, and presents distribution in a 4.88 mm range close to the beam waist. The calculation results show that the flatness of the beam in that range is below 0.1. It also shows that the signal combiner can handle a signal power of more than 2 kW.