I'm doing a research for my bachelor degree final project and it contains no experiments. I found a paper which has published results of an experiment and their data and images/diagrams are so relevant to the subject of my work. Is it kind of plagiarism if I use their data and images even with referencing to their paper?
If you cite their work, then it isn't plagiarism. You just make clear what things, especially ideas, came from them and which are your own. Plagiarism isn't about reuse, but about misattribution.
However, you may have to deal with copyright as well which will limit how much of what they say can be part of your paper. But quoting brief passages (with citation) is fine, as is pointing readers of your work to theirs.
Images, however, are a special copyright problem, since an image can be considered a "work" in its own right separate from the paper in which it occurs. To copy such images you may need to get permission from the copyright holder (as well as cite). You can create your own images from the original data, but not so similar as to be considered infringing.