  Darboux transformation is developed to systematically find variable
separation solutions for the Nizhnik-Novikov-Veselov equation. Starting from a
seed solution with some arbitrary functions, the once Darboux transformation
yields the variable separable solutions which can be obtained from the
truncated Painlev\'e analysis and the twice Darboux transformation leads to
some new variable separable solutions which are the generalization of the known
results obtained by using a guess ansatz to solve the generalized trilinear
equation.
