The embodiment of the invention discloses a trimming method of a shearing machine, which comprises the following steps: placing an aluminium coil blank installed on an inflation shaft on a recoiling machine; performing reverse trimming and waste edge output on the aluminium coil blank through all rolls and the shearing device of the shearing machine; reversely rolling the trimmed aluminium coil blank to a decoiler provided with a steel sleeve to produce aluminium products. The embodiment of the invention uses the existing shearing machine, utilizes the decoiler and the recoiling machine alternatively, realizes the trimming process of the aluminium coil blank, and overcomes the drawbacks that trimming can not be performed on the aluminium coil blank in prior art in case of no slitting machine or the fault and the busy operation of the slitting machine when the slitting machine is used for trimming, and the production supply of the aluminium products is difficult to guarantee.