If there is no theory in the undergraduate thesis, then we need to solve the problem from the following angles. First of all, we can check whether the papers written by undergraduates have theoretical basis to support his research conclusions, and if so, we can give relevant quotations and comments in the papers. Secondly, the theoretical support of the paper can be strengthened by searching and sorting out relevant literature. Finally, if you really can't find the relevant theoretical support, you can contact your tutor and seek other suggestions or opinions. In short, in the process of writing a thesis, theory is an important support, and it must be fully integrated into the thesis to make it more rigorous and convincing.