Tetragonal distortions,crystal structure,magnetism,electronic structure and pressure response of Hg2CuTi-type Mn2NiGe are calculated by the first-principles method based on the density functional theory. The calculations show that 1)in the process of transform from cubic to a tetragonal in structure,Mn2NiGe alloys exhibit a stable martensitic phase at c/ a≈1.34; 2)in austenite and martensite,Mn atoms are the main contributors to the magnetism in Mn2NiGe,and Mn2NiGe alloys show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn(A) atom and Mn(B) atom; 3)in austenite and martensite,the direct d-d exchange interaction between Mn(A) atom and Mn(B) atom is weak because of small overlap of d-projected DOS of Mn(A) atom and Mn(B) atom nearby the Fermi level. This is the reason why the Mn2NiGe alloys show ferrimagnetism. We can predict the magnetic shape memory effect (MSME) in Mn2NiGe alloys based on the the results of calculation above.