In　this　brief,　in　order　to　solve　the　discounted　optimal　tracking　control　problem　for　discrete-time　systems　with　control　constraints,　an　advanced　online　value　iteration　(VI)　algorithm　is　developed.　First,　we　revisit　discounted　general　value　iteration　(GVI)　for　optimal　tracking　control　design.　Second,　the　stability　condition　of　GVI　is　established,　which　can　be　applied　to　evaluate　the　current　iterative　tracking　control　policy.　Third,　based　on　the　concept　of　attraction　domain,　the　evolving　tracking　control　policies　generated　by　online　VI　can　be　obtained　through　judging　the　location　of　the　current　tracking　error.　Finally,　we　prove　system　stability　based　on　online　VI　for　the　present　tracking　control　problem.　A　simulation　example　is　shown　to　illustrate　the　effectiveness　of　the　developed　algorithm.