Korea Astronomy and Space Science Institute (KASI) has officially started a project to construct an astronomical widefield survey system, namely KMTNet (Korea Micro-lensing Telescope Network), from January 2009. Its primary scientific goal is to discover numerous extra-solar planets, especially earth-mass planets, using the gravitational microlensing technique. This goal requires continuous photometric observations with high cadence of about 10 minutes for tens of millions of stars in dense fields toward the Galactic bulge. KMTNet will comprise three identical systems at southern observatories with different time zones. Each observing system consists of a 1.6 m wide-field optical telescope and a 20k by 20k mosaic CCD camera, which covers a 2 by 2 degrees square field of view. In this proceeding, we present technical specifications, designs and fabrication schedule of the KMTNet system.