Inspector Robert Parry, who sat during the original inquiry from November 2003 to March 2005, will hear evidence from next February.
He will consider four specific issues including a possible alternative boundary from the north of Petersfield to Pulborough. He will also look at objections made over recommendations for land to be included in the park.
High Court and Court of Appeal judgements on the New Forest national park will have to be assessed, as will the effect of the National Environment and Rural Communities Act 2006.
A public consultation on the park was held earlier this year. DEFRA has asked Parry to indicate if any of his recommendations have been changed as a result of the evidence from this exercise.
The Council for National Parks and the South Downs Campaign (SDC) have welcomed the reopening of the inquiry. They stressed that the inspector needs to reconsider his recommendations on the park's boundary.
Both groups have argued that the Western Weald area in particular must be included in the park. The SDC said it is confident that the reasons for its exclusion will not stand up to scrutiny.