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All available mid-eclipse times of the eclipsing binary Z Draconis areanalysed, and three sets of cyclic variations with periods of 20.1, 29.96 and59.88 yr are found. The low-amplitude variations with the period of 20.1 yr maybe attributed to the unavoidable and slight imperfection in thedouble-Keplerian model, which gives the periods of 29.96 and 59.88 yr.Interestingly, the Z Draconis system is close to a 2:1 mean-motion resonance,or 6:3:2 mean-motion resonance if the period of 20.1 yr is true. We also findthat the best solutions tend to give the minimum eccentricities. Based onKepler's third law, the outermost companion has the minimum mass of$\sim0.77M_{\bigodot}$, whereas the middle companion is an M dwarf star with amass of $\sim0.40M_{\bigodot}$, suggesting that Z Draconis is a general N-bodysystem.

Z Draconis with two companions in a 2:1 mean-motion resonance