A transmission structure of a waist twirling exercise machine for body-building and a method thereof includes left and right stepping rods which are obliquely or horizontally connected to a machine base, left and right stepping platforms having left and right shafts inserting through lubricating members provided in through holes of the left and right stepping rods, left and right transmission members having first ends connected to the left and right shafts and second ends provided with eccentric blocks, left and right connecting rods having first ends connected to the eccentric blocks of the left and right transmission members and second ends pivotally connected to either of the machine base and pneumatic cylinders. When the left and right stepping platforms are treaded in turn, the left and right connecting rods subject to their lengths will drive the left and right stepping platforms to turn left and right in turn synchronously, enhancing a waist twirling effect.