Inspired by allosteric regulation of natural molecules, we present a rational design scheme to build synthetic nucleic acid allosteric nanodevices. The clearly specified conformational states of switches obtained from systematic screening and analyses make the ON-OFF transition clear-cut and quantification ready. Under the rational design scheme, we have developed a series of DNA switches with triplex-forming oligos as allosteric modulators and implemented designated allosteric transitions, allosteric coregulation, and reaction pathway control. In conjunction with toehold-mediated strand displacement, our design scheme has also been applied to synthetic nucleic acid computing including a set of logic operations and complex algorithm.