The point of sale (POS) system allows businesses to complete purchases, records sales data, and view business performance reports. So, it means that the POS is the time and place where a seller and buyer have completed transactions. There are five objectives of our thesis such as to the analysis of the whole process of using the POS web application system, to study the database structure of the POS system, how to develop the POS web application system software, to study about advantages and disadvantages of using the POS system, and to learn how to create a RESTfull web services API. Moreover, We have divided it into five main functions in our web application system such as dashboard, transaction, inventory, report, and setting. Especially, we have used the tools to develop our software products such as C# programming language, ASP.NET (POS web application), ASP.NET MVC (POS REST web service API), HTML5, CSS, Bootstrap, javaScript, and Microsoft SQL Server 2008R. Thanks in advance for your valuable time to read my thesis's work.