Porous aggregates were made from gangue and fly ash by sintering. X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury piezometer (MIP) were used to analyze the evolution of the physical phase composition, microscopic and pore structure of the aggregate during the sintering process. The results show that porous aggregates with cylinder compressive strength of 2.5MPa and thermal conductivity of 0.1416W/(m-K) were prepared from gangue and fly ash by preheating temperature of 500℃, preheating time of 20min, sintering temperature of 1000℃ and sintering time of 10min. When the sintering temperature was increased to 1200°C, mullite accumulated to form pores with r<1000nm. The medium and large pores are covered by a liquid phase with an average thickness of about 0.466μm, which reduces porosity by 7.29% and increases the cylinder compressive strength. The high thermal conductivity of mullite and the reduction of the average pore size lead to the increase of thermal conductivity.Carbon emissions from the porous aggregate in 1m3 of concrete is 140.2KgCO2, which is 56.2% and 56.3% lower than that of the Stalite aggregates and fly ash lightweight aggregate, has more green potential.