Grid computing has gained great success in harnessing computing resources. But its progress of gridfication on scientific computing is slower than anticipation. This paper analyzes these reasons of hard gridification in detail. While cloud computing as a new paradigm shows its advantages for its many good features such as lost cost, pay by use, easy of use and non trivial Qos. Based on analysis on existing cloud paradigm, a cloud platform architecture based on YML for scientific computing is presented. Emulations testify we are on the right way to extending YML to be middleware for cloud computing. Finally on going improvements on YML and open problem are also presented in this paper.