Atomic orbitals have many advantages as basis sets for ab initio electronic structure calculations.They have been popular in recently developed fist-principles simulation packages.However, the atomic basis sets must be constructed very carefully to ensure both good accuracy and transferability.Furthermore, the quality of the basis sets should be systematically improvable in an unbiased way.We have proposed a unique scheme to construct systematically improvable optimized atomic basis sets.This scheme has been implemented in our home made first-principles packages.We introduce our large-scale ab initio simulation package based on the systematically improvable atomic basis.Our benchmark tests show that our atomic bases work very well for wide range of physical systems, including bulks, molecules,surfaces, defects, etc.