With the development of Internet, More and more people are participating in the electronic commerce activity through the web and the transaction over the net is becoming a kind of human life style. But, because of the fault of Internet itself, there exist much security problem during the electronic payment. The searchers are studying harder to design a more secure and effective electronic payment to break through the limitation of the electronic commerce at present and to make better use of the modern network technology to implement a prevalent, daily and subsistent transaction on the net.It is known that there would not be an available electronic commerce system without an effective electronic payment through the web. Now lots of protocols and schemes on electronic transaction have been proposed and positively solved some problems. But the electronic payments, also called electronic money, in those schemes still have some disadvantages, especially in aspect of the divisibility. And in this paper, they will be solved.Firstly, the conception and development of the electronic payment over network is introduced, and then three kinds of electronic money are discussed on their advantages and disadvantages. Secondly, some security technologies used in the electronic payment are accounted for. Finally, a notion ofPersonal Electronic Money(PEM) is proposed. A new simple and available on line electronic payment scheme based on PEM is also designed. The scheme can solve the divisibility problem about traditional electronic money and enable client use random electronic money in transaction through the web. And the scheme has high security.