In teaching Mathematics in primary school, mental arithmetic and writing calculation are very important and It is always paying attention to students. The 2018 Math program has focused on mental arithmetic skills in parallel with training in writing calculation skills. This paper mentiones the training of mental arithmetic skills for 2nd grade students in teaching Mathematics ensures the required requirements of the program, and at the same time contributes to the realization of primary education goals. In this paper, we propose several techniques for addition and subtraction mental arithmetic within 20, and addition and subtraction of whole hundred numbers within 1000.