The interaction between dark solitons in nonlocal self-defocusing media is investigated. Numerical results show that there is a critical condition for interaction between dark solitons in nonlocal self-defocusing medium. Under the critical condition, dark solitons will neither attract nor repell each other because the attractive force and repulsive force between them are identical. Beyound the critical condition, dark solitons may attract or repell each other depending on the nonlocalization degree and distance between them. The value of the critical condition is found.