Patrick Sheehan cited "irreconcilable differences" with his wife of 28 years, Cindy Sheehan, who has demanded Mr Bush withdraws US troops from Iraq.
The couple's eldest son, Casey, was killed in action in 2004. Mrs Sheehan has pledged to stay in Crawford until the president agrees to meet her.
Mr Sheehan claims he is owed a share of money awarded after Casey's death.
He filed for divorce in a court in San Francisco on 12 August, according to papers released into the public domain.
Determined protest
The couple, who have been together since their high school days, have been separated since 1 June.
They say that the stress of dealing with their son's death has undermined their relationship.
Mrs Sheehan says she plans to remain in Crawford throughout Mr Bush's summer holiday at the ranch, where about 100 anti-war activist have joined her vigil.
The president has so far refused to meet Mrs Sheehan, although he says he has given her plea for troop withdrawal serious consideration.
White House officials have pointed out that Mrs Sheehan met the president on a previous occasion, and made her views known on that occasion.
She has complained that the president was disrespectful towards her, and says their previous meeting came before revelations of faulty intelligence-gathering in the run-up to war.
