Abstract: The hole stability of ex tended reach well is very important to the safety drilling of the ocean oilgas development process. Based on the lithomechanics mechanism of the extended reach well hole stability, the paper analyzed the stress state of the wallrock, established the isotropic linear elasticity mechanical model of ocean extended reach well stability based on the characteristics of crustal rock, and presented the hole collapse and fracture condition of extended reach well based on the Coulomb-Moore strength criteria and the maximum tension stress fracture criteria. The windows software for the mechanics stability analysis of extended reach well was compiled using the Visual Basic. The factors of extended reach well hole stability was analyzed with this software, and the hole collapse pressure of extended reach well was quantitative estimates. The calculation for the field data of one of the gas fields of East China Sea shown that there is direct relationship between the hole collapse pressure of extended reach well and inclination, drift azimuth. And the variation law of the hole collapse pressure of extended reach well along with hole angle and azimuth mostly decided by the status of the stratigraphic in-situ stress.