The paper is written with the hope that through collection, comparison and analysis the common errors and mistakes which students in Hai Phong University often make when thay study “de” in order to learn about the error, arising rate and types of errors anhs mistakes students use them, as well as find out the cause of making error and mistakes. Form that,some solutions are given to solve the problems with the expectatinon that students will make less errors and mistakes than before.