Abstract: Based on the gently inclined medium thick phosphate deposit at the east mining section of +2 150 m level of Jinning No.6 mine under Yunnan phosphate Co.，Ltd.，the similar simulation experiment of the stability of stopes pillars under room and pillar mining was carried out by the similarity simulation of mine pressure plane stress modeling.Based on the experimental results，the stress changing law of the above roof of stope pillar during the mining along the strike direction of phosphate were investigated.The macroscopic instability and failure model and instability mechanism were also studied.Then，the stope structural parameters under the room and pillar mining method are optimized.The experimental results showed：The deformation and breaking features of stope wall rock under room and pillar mining method has obvious three phase characteristics.The overburden rocks are divided into caving belt，fissure zone，micro cracks loose belt according to the deformation level.After the ore body excavation finished，individual pillars are recovered.After that，the whole instability and large-scale failure of mining pillar may suddenly occur，called obviously domino effect phenomenon.At the same time，the stope structural parameters of 10 m room and 8 m pillar are recommended so as to ensure the mining safety.The relevant research can provide theoretical and technical guidance for the underground mining of the deep ore body or similar mines.

Key words: Gently inclined and medium thick phosphate rock, Stability of pillar, Pillar and room caving, Similar simulation, Stope structure parameters, Optimization