The invention discloses a method for adjusting a gap of blades of a pair of crank flying shears and a device thereof. An upper set of eccentric adjustment mechanism and a lower set of eccentric adjustment mechanism are arranged on a stander of the crank flying shears, and are respectively connected with an upper knife rest and a lower knife rest, and the upper knife rest and the lower knife rest are respectively driven by the upper set of eccentric adjustment mechanism and the lower set of eccentric adjustment mechanism to move at the same direction or the reverse direction, so that the gap of the blades on the upper knife rest and the lower knife rest is reduced or enlarged, the time for adjusting the gap of the blades of the shears is effectively reduced, the method is convenient to operate, the precise adjustment is easily realized, and the production efficiency is improved.