To effectively develop heavy oil with apparent viscosity above 150 mPa·s in-situ, a heavy oil activator was designed and applied in the field, which can efficiently increase the viscosity of aqueous phase and the mobility of oil phase. The wettability, interfacial properties and the microscopic dispersion of oil with activator were measured using the contact angle meter and laser scanning confocal microscopy. Experimental results showed that the contact angle between activator and heavy oil was 34.67° and the oil-water interfacial tension could be reduced to 0.1 mN/m by adding activator. Furthermore, it was clearly observed that the crude oil was uniformly dispersed into small drops. For the hybrid system consisting of 660 mPa's crude oil and 1000 mg/L activator with a mixed ratio of 1:1 by volume, the flowing time measured by kinematic viscometers was reduced to 8 s compared with 340 s of single oil system. By adopting the activator flooding, laboratory experimental studies showed the recovery of heavy oil could be enhanced by 14.3% on the basis of water flooding. The change of oil-water front and distribution of saturation field confirmed that the activator had the ability to disperse heavy oil and improve the micro-displacement efficiency, and the contribution rate accounted for about 28% of the total recovery. This obvious effect has been successfully achieved in pilot test of both S Oilfield and D Oilfield. By applying activator huff and puff in S Oilfield for 14months, the total incremental oil reached 44,952 bbl tons. And using activator of 800 mg/L to exploit heavy oil with viscosity of 1170 mPa·s in-situ at 35 °C. After 3 years of injection, the cumulative incremental oil of D oilfield was larger than 120,000 bbl, which means that each ton of activator can ramp up production of 660 barrels oil.