Most experts and critics agree that Oedipus' tragic flaw is his hubris, or excessive pride, which leads to his metaphorical blindness throughout the play, and of course, ultimately his demise. Consider all of the ways in which pride lead to his downfall. First, in response to Teiresias' first message (while living in Corinth) that he should one day kill his father and marry his mother, Oedipus pridefully sets out to prove the prophet wrong. This leads him to a crossroads where, in a bout of pride and anger, he kills the old man (his real father). Once he becomes the king of Thebes, he refuses to listen to those who attempt to help him, including Teiresias (again) and Creon. When the hidden secret becomes fully apparent to Oedipus, namely, that he is the plague poisoning the kingdom, his final act of pride is to physically blind himself so that he will no longer have to look on himself in shame.
You could certainly do a more detailed examination of Oedipus' decisions throughout the play and likely come up with more than one tragic flaw, but likely each one could be rooted in excessive pride.