No matter which university you go to, you're bound to come across these words: paper, dissertation and thesis. Most likely you're doing one right now. So are there any differences between these academic words? Even though they are the same word in Chinese, they are different in the depth of research and the level of analysis.
The word 'paper' is American English. In British English we say 'essay'. Papers or essays are generally related to undergraduate degrees. The word 'thesis' is generally associated with the final piece of writing for a PhD student. A 'dissertation' is for a master's degree.
However, in the United States the reverse is true. The final doctorate paper is called a dissertation and the master's degree requires a thesis.

来源：http://edu.qq.com/a/20131104/013007.htm