Focusing on spindle box of TBTML500 deep-hole drilling machine,considering the influence of stochastic factors,the structural lightweight design considering the reliability and stability requirements was performed by using the reliability topology optimization design method based on the variable density method.The probability constraint was added to the traditional topology optimization model under the stress and displacement constraints;the reliability topology optimization problem was decoupled into the reliability analysis and deterministic topology optimization by the first-order reliability method and the Roenblatt inverse transformation. Finally,the variable density topology optimization was performed.The example analysis results show that this method better meets the safety requirements in the practical application while realizing the lightweight,and also provides a reference for the reliability topology optimization of other basic parts of the deep hole drill bed.