One double-channel output structure of spiral PFL(pulse forming line) with an outer shield and an inner cylinder is presented. This kind of spiral PFL comprises a high-coupling Tesla transformer with built-in ferromagnetic material as the inner and the outer cylinders. When the secondary channel outputs pulses in a matched way, the flat-topped fluctuation of the main pulse will be removed, and most of the stored energy will be delivered to the main load. The problem of the spiral line put forward by Korovin can thus be resolved. The comparison of two technical methods, the double-channel spiral-PFL one and the one applied in SINUS-700/130, shows that the flatness of the output pulse for the former is better and the output power increases by 29%, whereas the secondary load will consume 11%