The South African Development Community has called for reforms ahead of the July 31 election.
Mugabe , 89, told members of his Zanu-PF party the reforms would not be accepted automatically.
"Let it be known that we are in SADC voluntarily; if SADC decides to do stupid things we can move out and withdraw from SADC," Mugabe said at Saturday's rally in Highfields.
Mugabe told his audience to be prepared for a "battle for survival," but also said he expected a 90-percent victory for Zanu-PF.
Such a wide margin would likely bring an end to the current coalition government and leave Mugabe and his supporters once again in firm control of Zimbabwe, the BBC said.
Mugabe is running against Prime Minister Morgan Tsvangiari, a longtime rival who won the first round of the election. Mugabe bounced back with 85 percent of the vote in the second round.