After more than 30 years of the only-child policy, China has a great amount of only-child families. Using the 1% sample data of population survey in 2005 and the census data of 1990, 2000 and 2010, we take the target population of the new family planning policy as research goal, and simulate the population structure of 2010 and set up a simulating data base for 2010 by computer. From the simulating data base, we estimate the population size and structure of the fertility women of the 2-child policy for only-child parents by rural and non-rural, and east, middle and west regions. We find that about 14 million families will be covered by the new 2-child policy for only-child parents. The mainly target families concentrate in the east part of China: the number of families is about 7 million, and there are about 5.3 million non-rural families among these families. There are 4 million and 3. 2 million target families in the middle and the west respectively. The authors also analyzed the possible problems posed by the new policy and proposed some policy suggestions.