Analysts believe Jong-il's youngest son Kim Jong-un is likely to be given an official title at the Workers' Party conference.
That would pave the way for his eventual succession as leader.
Jong-il, who is believed to have suffered a stroke in 2008, has reportedly accelerated succession plans.
The North's KCNA news agency said the conference would be held in Pyongyang "for electing its supreme leadership body", but provided no further details of the agenda.
The meeting had been due to start in early September. The report made no mention of the delay.
South Korea said it appeared the meeting was held up by "internal problems", probably related to flooding.
Media reports have also speculated Kim's health or disagreements over a reshuffle of the power structure could be responsible for the delay.
Party meetings have been held around the country to elect delegates to conference, KCNA reported.
"The meetings elected working people and officials who have displayed patriotic devotion at the work sites for effecting a fresh revolutionary surge, remaining intensely loyal to the party and revolution as delegates to the conference," it said.
Next week's meeting will be the biggest political meeting in North Korea since 1980, when Jong-il himself began his official role.
He succeeded his father and state founder by taking on a Workers' Party title at the age of 38.
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