Abstract: We have constructed the robust and high-field-stability scanning tunneling microscopy (STM) system which is equipped with a 12 T-superconductor magnet and the He-3 cryostat, obtaining the high-quality data of graphite which can be clearly characterized up to the 12-T high magnetic field and bulk 2H-NbSe₂ whose vortex structure and surface defects can be clearly visualized by the scanning and dI/dV mapping. The pivotal factor of our superior data stems from the sapphire frame and its unique structure, which ensure an exceptional performance for the noise, which has the current spectral density low to 2×10⁻¹³ \mathrmA/\sqrt\mathrmHz at the low frequency with the cut-off frequency of 250 Hz and the engaging status, of vibration, promising to the robust platform for the investigation of the surface of materials. The low drifting rate from the image of graphite is v_x= -8.79\times 10^-7\;\rmnm/s and v_y= -3.26\times 10^-6\;\rmnm/s at 12 T and 0.3 K. Besides, equipped with the high-capacity (volume of He-3 gas is 15 normal temperature and pressure liter) He-3 cryostat, the system, which has the base temperature for 0.28 K, can operate at the low temperature for more than 72 h, ensuring the enduring research at the sub-Kelvin temperature for the dI/dV mapping and large-scale scanning. When the magnetic field is applied up to 12 T, the STM system also obtains the excellent-clarity and undistorted images of graphite, which proves the outstanding performance of the system at the high-field researches.