To learn number system is a basic thing in school mathematics. In this paper, we analyze how number system is introduced in the 7th national curriculum and text books according to it. We found that the method of introducing number system is quite different from the former curriculum and former text books. There are many negative effects on the transition when compared with those of United States of America. There are many gaps between elementary school mathematics and middle school mathematics about levels and skills to deal with numbers. It is desirable to distinguish the negative sign from subtraction and to keep the concepts of commutativity and associativity of operations from the beginning. We also suggest to change the introducing timing and extension methods of number system in 7th grade mathematics.