Abstract: In order to improve the efficiency of coal-fired units participating in system regulation, promote the penetration rate of renewable energy and achieve the low-carbon transition of the power system, two cooperative operation optimization models were constructed from the perspective of coal-fired units system. One was aiming at low carbon for overall operation, and the other was aimming at economic for overall operation. In the two models, the cooperative effect of coal-fired units with different technical characteristics was explored under high penetration rate of renewable energy. Case study indicated that the cooperative operation of units based on low-carbon objectives was conducive to giving play to the advantages of high-performance units. Small-capacity, low-parameter units generated less power and mainly provided auxiliary services. It effectively reduced the total carbon emissions of coal-fired units while improving the penetration rate of renewable energy. However, the overall economics of the units would be affected. As the penetration rate of renewable energy increases, the effection of cooperative emission reduction would be significantly enhanced. The design of future power system should fully consider the cooperation between the units with different technical characteristics.