Abstract: Radioimmunotherapy(RIT), a kind of internal radiation therapy, can achieve high performance and low toxicity by fewer monoclonal antibodys couple radioactive nuclides, created sufficient ionization biologic effect on tumor. B cell lymphomas has higher relapsed rate, CD20 is the best target of RIT on B cell lymphomas because the expression rate of it on B cell lymphomas is above 90%, and it is not desquamated easily. There are severy drug of RIT, such as ¹³¹I-tositumomab, ¹³¹I-Rituximab, and ⁹⁰Y-ibritumomab tiuxetan. Each one has its advantages and disadvantages. Clinical trials indicates they are effective on B cell lymphomas, and safe to non-targetted organs. The main side effects include thrombopenia, neutropenia, gastrointestinal tract response, and hypothyroidism. While satisfied results have attained, many problems are existed. All researchers do their best to resolve there problems for better therapy results.