Abstract: In order to investigate the characteristics ofthermocapillary flow instability, thermocapillary convection is investigatedwith three-dimensional numerical simulation in a shallow annular pool (depthd =1mm) of silicone oil (0.65cSt, Pr= 6.7) with the heated inner walland the cooled outer wall. The numerical results show that, surface temperaturegradient in the pool heated from inner wall is 10% higher than thatheated from outer wall with a fixed temperature difference between the outerand inner walls. Meanwhile, the critical Marangoni number for the incipienceof hydrothermal wave (Ma_c=3.06\times 10^5) in the pool heated frominner wall is smaller than that (Ma_c=3.34\times 10^5) heated fromouter wall. Furthermore, numerical results indicate the oscillatorymulticellular wave in the pool heated from inner wall when Ma exceedsMa_c. The oscillatory multicellular wave is composed of two hydrothermalwaves propagating in opposite azimuthal directions, which are interferedeach other to be dot ripple.