The Zhaoshan long-baseline Atom Interferometer Gravitation Antenna (ZAIGA) is a new, to the best of our knowledge, type of large-scale atom interferometer facility under construction for the study of gravitation and related problems. To meet the different requirements of the laser system for the atom interferometer using various atoms (including 85Rb, 87Rb, 87Sr, and 88Sr), we design and implement a modular assembled laser system. By dividing the laser system into different basic units according to their functions and modularizing each unit, the laser system is made highly scalable while being compact and stable. Its intensity stability is better than 0.1% in 102s and 0.5% in 104s. We test the performance of the laser system with two experimental systems, i.e., an 85Rb-87Rb dual-species ultracold atom source and an 85Rb atom interferometer. The 85Rb-87Rb dual-species magneto-optical trap and the 85Rb atom interference fringes are realized by using this laser system, indicating that its technical performance can meet the major experimental requirements.