Abstract: Oil production is often greatly affected by the collapse of well casings under the super-high pressure of the soft rock under deep layer，Aiming of this，the authors in this paper base their discussion on the thick tube theory in the elasticity mechanics and the optimization theory and put forward a new approach towards the optimization design of the pipe-in-pipe combination to resist the super-high pressure of the soft rock under deep layer.

Key words: Pipe-in-pipe, Collapsing strength, Force transmitting, constant Opti-mization design, SJMT method