[en] Nanotwinned Mg nanopillars under uniaxial compression were investigated by molecular dynamics simulations. The simulation results indicate that more $\{10\stackrel{¯<!--\; ??\; -->}{1}1\}⟨<!--\; ???\; -->10\stackrel{¯<!--\; ??\; -->}{1}\stackrel{¯<!--\; ??\; -->}{2}⟩<!--\; ???\; -->$ TBs and less $\{10\stackrel{¯<!--\; ??\; -->}{1}2\}⟨<!--\; ???\; -->10\stackrel{¯<!--\; ??\; -->}{1}\stackrel{¯<!--\; ??\; -->}{1}⟩<!--\; ???\; -->$ TBs are recommended to introduce for obtaining Mg nanopillars being of higher compressive yield strength. The pre-built $\{10\stackrel{¯<!--\; ??\; -->}{1}1\}⟨<!--\; ???\; -->10\stackrel{¯<!--\; ??\; -->}{1}\stackrel{¯<!--\; ??\; -->}{2}⟩<!--\; ???\; -->$ TBs restrains the nucleation of new twins, and subsequently causes the increase of the yield strength. The initial yield behavior of nanotwinned Mg nanopillars with $\{10\stackrel{¯<!--\; ??\; -->}{1}1\}⟨<!--\; ???\; -->10\stackrel{¯<!--\; ??\; -->}{1}\stackrel{¯<!--\; ??\; -->}{2}⟩<!--\; ???\; -->$ TBs was found to be twinning nucleation, and the nucleation mechanism is a shuffling mechanism. The introduction of $\{10\stackrel{¯<!--\; ??\; -->}{1}2\}⟨<!--\; ???\; -->10\stackrel{¯<!--\; ??\; -->}{1}\stackrel{¯<!--\; ??\; -->}{1}⟩<!--\; ???\; -->$ TBs bring sources of dislocations into Mg nanopillars and subsequently causes the decrease of yield strength. (paper)