You can take a 5-foot step as part of your readied action, but only
if you don’t otherwise move any distance during the round. For
instance, if you move up to an open door and then ready an action to
swing your sword at whatever comes near, you can’t take a 5-foot
step along with the readied action (since you’ve already moved in
this round).
不好意思,顺便给个PHB原文