As a Lie n-groupoid is an atlas for an n-stack in differential geometry, one expects that their differentiation should be the tangent complex of the n-stack carrying a Lie n-algebroid structure. However, an explicit differentiation, like that for Lie groupoid, seems to be missing. Inspired by Severa's idea of an infinitesimal object, we perform (spending a lot of years fixing holes :) an explicit differentiation, and reach the tangent complex with a Lie n-algebroid structure. This is a joint work with Du Li, Rui Fernandes, Leonid Ryvkin and Arne Wessel.