Mastering vocabulary is an important thing because, without it, we don't understand the text. Further, we can't speak if lack of vocabulary. In contrast, English is a unique language because one word can different meaning in a different context. So, understand the context is important too. In addition, computer science students should understand the specific vocabulary related to their field. But, more of them difficult to understand because don't know the specific meaning. This study aimed at how to improve mastering vocabularies for computer science through reflecting. It was a qualitative descriptive approach. Data collection method was documentation through photovoice and test result. The analysis was documentation analysis. A sample of data was computer science students in second grade. The result was photovoice could represent what students' problem and reflection they knew the mistake so, they can improve mastering vocabulary in computer science.