The diffraction contrast method for studying dislocations in quasi-crystals is discussed and summarized. As a general principle, by finding five linearly independent extinction reflections g_i (i=1, 2, 3, 4, 5), under which the dislocation contrast is invisible, the direction of the Burgers vector b of a dislocation in an icosahedral quasi-crystal is determined to be the vector product of these five reciprocal vectors. By applying this method we determined the Burgers vector b of a dislocation in an Al₇₀Pd₂₀Mn₁₀ icosahedral quasi-crystal to be parallel to the six-dimensional vector (2-10-20-1) which possesses a rather large phason component.