Officials in southern Sudan cited the north's veto of ethnicity and religion on the census questionnaires as a reason for the initial refusal.
But UN overseers said on Sunday that both sides agreed on the compromise formula.
Gabriel Changson Chang, information minister in the southern government, said: "Sudan is an African country because the majority of Sudanese people are Africans, which contradicts directly the claim we are an Arab nation.
"This can only be proved through an objective exercise like the census."
The Arab domination of power in what is Africa's largest country was a major reason for the two-decade civil war between north and south, as well as for the separate five-year conflict in western Sudan's Darfur region.
Riek Machar, vice-president of South Sudan, said that the north and south need to address questions of race and identity.
"Ethnicity and religion are crucial issues. They address the identity of Sudan, he said.
"Our wars are based on [the question:] What is Sudan?"
Chang also said two million displaced southerners living in the north must be given the option to be repatriated to the south before the census, otherwise the count would disadvantage them.
"The government of South Sudan will take measures to make sure they are repatriated before the census is carried out ... There is undue influence in Khartoum in preventing the IDPs [internally displaced persons] from coming back to the south," Chang said.
He said that various disputes with the north, which he said have not been resolved under a timetable to implement the 2005 peace deal, must be addressed or completed before the south approves the population count.
"There is no peaceful atmosphere. Why don't we talk about those pending issues, the border issues, Abyei [an oil-rich area claimed by both north and south where tensions have risen in recent weeks], Darfur?" Chang said.