To　solve　the　tracking　control　problem　for　nonaffine　systems,　an　online　design　method　was　developed　by　using　the　action　dependent　heuristic　dynamic　programming　(ADHDP)　structure.　Firstly,　the　tracking　control　problem　for　the　unknown　nonaffine　system　was　transformed　into　the　error　regulation　problem.　Then,　the　ADHDP　tracking　controller　was　designed　and　the　online　learning　method　was　adopted　to　synchronize　the　system　control　with　the　training　of　action　networks　and　critic　networks,　so　that　the　desired　trajectory　could　be　tracked　by　the　system　state.　Finally,　a　simulation　example　was　given　to　verify　the　effectiveness　of　the　proposed　method.　©　2022　Chinese　Journal　of　Intelligent　Science　and　Technology.　All　Rights　Reserved.