To improve the stability of the atmospheric inductively coupled plasma (ICP) torch, a demountable ICP torch whose dielectric tubes were located by a special part was designed, and its heat transfer and flow characteristics were studied. Through the simulation by COMSOL Multiphysics, it is found that the annular heating and fluid backflow are the main reasons for thermal damage and etching damage of the torch. Therefore, the service life of the torch can be effectively improved by using ceramics as the material of the central and middle dielectric tubes and adjusting the position of the induction coil. In addition, the jet morphology was monitored by a CCD camera. It is found that the overall length (L) and the half-width (W) of the jet linearly changes with the radio frequency power (P_w), the working gas flow (Q₂) and the cooling gas flow (Q₃). However, when the P_w, Q₂ and Q₃ are too big or small, the fluctuation of the jet increases, the ICP jet will become unstable. The results show that when P_w, Q₂ and Q₃ are set to 900-1 000 W, 650 mL·min^-1 and 16 L·min^-1 respectively, the demountable torch can generate stable ICP jet. The fluctuation of L and W can be controlled within 0.5 mm and 0.25 mm respectively, which is suitable for the processing of fused quartz and other optical surfaces.