Molecular dynamics simulation of the impact of disulfide bond on the conformational stability of native and reduced insulin was conducted at all-atom level.It was shown that disulfide bond restricted the relative motion of chain A and chain B in native insulin and thus strengthened the conformational stability for both the domain and active site.For reduced insulin without the native disulfide bonds，the conformation of the activate site altered while chain A and chain B dissociated.Moreover，the simulation suggested that the central helix in chain B would be unstable after disengaging the disulfide bonds，i.e.，the deactivation was irreversible.The above described simulation reproduced the experimental observations reported in the literatures，and established a molecular insight into the impact of disulfide bonds on the conformational stability of insulin，and would be of fundamental importance to the processing，formulating and pharmaceutical application of insulin.