The thermal stability of $alpha$-, $beta$-, 6,6,12-graphyne and graphdiyne was studied by a statistic model, which was seriously tested by classical molecular dynamics simulations. By first-principles calculations of related potential energy curves,
the model predicts that all the lifetime of free-standing single layer graphynes considered is more than 10$^{44}$ years at room temperature. When the temperature gets up to 1000 K, they are still very stable, but quickly turn into graphene if the temperature is about 2000 K
