"The accident was that I discharged my firearm because I believed an intruder was coming to attack me," Pistorius said during his trial on a charge of having killed his girlfriend deliberately.
"The discharge was accidental," Pistorius said under cross-examination from Prosecutor Gerrie Nel who asked what the accident was.
In his plea explanation Pistorius said the shooting was an accident.
Pistorius shot dead Steenkamp through a locked toilet door in his Pretoria home on 14 February last year.
He says he mistook her for an intruder and has pleaded not guilty.
Pistorius told the court on Wednesday he never intended to shoot anyone.
"I never intended to shoot anyone. I got a fright from the noise inside the toilet," he said.
Nel asked the athlete if he fired his gun at intruders.
Pistorius responded: "I wasn't meaning to shoot anyone... I went to bathroom to protect myself... and Reeva.
"I got to the door I was unsure if there we someone on the ladder or behind the door... My intend was not to discharge my firearm."
He said he never intended to shoot anyone and got frightened.
Nel disrupted Pistorius and said he had an opportunity to give his version and now had to answer questions.
Pistorius responded: "My lady I believed someone was coming out to attack me. Out of fear I didn't have time to think I and discharged my firearm. I didn't intend to shoot at anyone."
Pistorius stuck to his story and said he didn't intend to shoot anyone but heard a noise from the toilet.
"I didn't have time to think about what I was doing," he said.
He also faces two charges related to contravening the Firearms Control Act, to which he has denied guilt.