The development of heavy oil reservoirs in Shengli Oilfield is dominated by thermal huff and puff and water flooding. The oil-to-steam ratio decreases by rounds and the remaining oil between wells is difficult to produce effectively in thermal recovery heavy reservoirs；it is not economical to drill new wells. The oil-to-water mobility ratio is high and the operating cost per ton of oil increases in water flooding heavy oil reservoirs，worsening the economic benefit and leading to a recovery factor of less than 20%. Since“The thirteenth Five-Year Plan Period in 2016-2020”，the technical idea of additive，synergistic，and balanced displacement was devised to improve the development effect of low-efficiency heavy oil reservoirs and enhance mobility and oil recovery through multi-stage profile control and chemical viscosity reduction. According to the study of viscosity mechanism of heavy oil，the research on depolymerization and emulsification mechanisms of viscosity reducer was deepened，and the compound mechanisms with chemical viscosity reduction were investigated，such as multi-stage profile control and flooding，anti-swelling，and gas solubilization. Key chemical agents such as oligomeric viscosity reducer and viscoelastic emulsification profile control and flooding agents and dual-function foaming agents were developed，and the decision-making and control technology for scheme optimization was improved，thus forming the compound flooding technology of heavy-oil chemical viscosity reduction with“strong profile control and flooding，viscosity reduction，anti-swelling，activity，and solubilization”as the core. Different from the“binary”and the“ternary”polymer flooding of conventional thin oil and the chemical flooding of common heavy oil，this technology has been successfully promoted and applied to various types of heavy oil reservoirs，such as those after multi-round huff and puff，sensitive，and high-temperature high-salinity water-drive ones，covering a geological reserve of 15 million tons. It is expected to increase the recovery factor by more than 8%，which effectively supports the transformational and beneficial development of low-efficiency heavy oil reservoirs.