Can i directly join uni. of texas at arlington after GRE/TOEFL?

Directly, no. You would need to be accepted by that program and would have to be finishing your bachelor's degree at your current institution before that would happen. You cannot go into a master's program without having first completed your master's degree, no matter how early you take the GRE/TOEFL and how well you may do on them. I should also note that most graduate programs are competitive, so you would have to do well to be accepted to that program over the others who apply.