In order to cooperate with the Chinese TG-2 space experiment project, this paper studies the flow structure and critical conditions at the onset of transition and nonlinear regimes of bouyant-thermocapillary convection in large-scale liquid bridge with large Prandtl number under normal gravity. The surface temperature distribution is obtained by means of thermal infrared camera, to study the temperature oscillation, temporal-spatial analysis and modal structures of the temperature field. In addition, the fluid velocity field is measured by Particle Image Velocimetry, to study the internal flow field structure and flow characteristics in the transition process of the liquid bridge. It is found that the critical value of the buoyant-thermocapillary convection in the half-zone liquid bridge can be affected by geometric parameters. Under large Prandtl number conditions, the critical temperature difference will change non linearly with the volume ratio, and the convection will transit from steady flow to a sequence of instabilities. In addition, various wave patterns will appear with increasing Marangoni number, and with further increased temperature difference a chaos state will emerge. (C) 2017 Elsevier Ltd. All rights reserved.