The invention relates to a conical pipe forming machine and a using method thereof. The conical pipe forming machine comprises a shell, worms evenly distributed on the circumference of the shell, and an intermediate wheel engaged with a gear at the end part of the worm, wherein the interior of the shell is provided with a variable diameter wheel seat in which a variable diameter wheel is hinged by a connecting piece, and one end of the variable diameter wheel is engaged with the worm. The using method comprises the following steps: fixing the forming machine on a workbench, and connecting oneintermediate wheel and a variable speed motor; coiling one end of an iron material on a columned iron core and fixing the iron core, wherein the diameter of the iron core is equal to that of a central hole formed by an A point of the variable diameter wheel; making the iron core pass through the central hole, and fixing the iron core with a broaching machine; switching on a power supply, and adjusting the drawing speed of the broaching machine and the revolution speed of the intermediate wheel; and during the drawing of the broaching machine, rotating the variable diameter wheel from the A point to a B point, and drawing a formed conical pipe into conical shape along with variation of the diameter of the variable diameter wheel. The conical pipe forming machine and the using method utilize the drawing principle for the first time to manufacture the variable diameter conical pipe, and have the advantages of low equipment cost, high production efficiency, high yield, good product quality, and high surface smoothness.