Barry Steenkamp said Pistorius must be going through a difficult time after the model was shot dead at the Blade Runner's Pretoria home last week.
He said the family was struggling to come to terms with the death, but revealed: "There is no hatred in our hearts."
He added: "He must be going through things that we don't know about."
Pistorius's father said he has no doubt the death was a tragic accident and that his son may have acted on instinct.
Miss Steenkamp was shot dead at Pistorius's home on Thursday – Valentine's Day.
Pistorius was remanded to a Pretoria police station after a hearing on Friday at which prosecutors said they intended to pursue a case of premeditated murder.
His family has already issued a statement in which they vowed to fight the murder charge in the strongest terms.
Pistorius will appear in court tomorrow for a bail hearing, something police have said they oppose.
Prosecutors also say they will pursue upgraded charges of premeditated murder against him, which means the athletics hero could face a life sentence.