A method of making a T-shaped pipe connecting device without a separate seam by using a unit body is provided to use no welding or casting method, simplify the structure and effectively increase the strength. The T-shaped pipe connecting device has no seamed part, does not corrode by a change of climate and temperature and easily break when used for a long period of time and is useful for building a plastic green house(vinyl house). The pipe connecting device is manufactured by the following steps: making the body(10) of a pipe connecting device by cutting a structural pipe(11) into a predetermined length and then forming a through-hole with a predetermined size on both upper ends of the body; enlarging the through-hole(20) to a predetermined size; forming an upper guide by forming an incision with a predetermined length on the front and rear surface of the upper end of the body and bending the upper surface of the upper end of the body and bending the upper surface of the through-hole at a 90 deg. angle; and
