  The purpose of this paper is to prove the a priori estimates for constant
scalar curvature Kaehler metrics with conic singularities along normal
crossing divisors. The zero order estimates are proved by a reformulated
version of Alexandrov's maximum principle. The higher order estimates follow
from Chen-Cheng's frame work, equipped with new techniques to handle the
singularities. Finally, we extend these estimates to the twisted equations.
