Bio-oil from biomass is considered a promising fuel candidate due to its high energy density. The organic molecules in bio-oil (heavy bio-oil) that are highly viscous and corrosive are the main obstacles to the industrial application of this oil. A mixture of methanol and n-octanol with a mass fraction of 25% was added to the oil as a solvent, and the mixture was blended via ultrasonic treatment to improve the quality and combustion properties of the heavy bio-oil obtained from pine nut shell pyrolysis. The effects of the ultrasonic power and time on the properties of the blend were studied, and the results showed that the heavy bio-oil blend had a superior higher heating value of 34.18 MJ/kg and a viscosity of 260 mPa s when the ultrasonic time was 11 min and the power was 55 W/L. Moreover, there was no stratification in the heavy bio-oil blend after 112 days of storage, and the moisture content and pH of the blend remained relatively constant. A model system that mimiced the heavy bio-oil was subjected to ultrasonic treatment and mechanical agitation, and the results of these experiments were compared. Alkenes that were not found in the untreated heavy bio-oil or in the mechanically agitated sample were observed following ultrasonication. Ultrasonic treatment could efficiently inhibit aging reactions and promote ring-opening reactions in heavy bio-oil blends to produce alkenes, thereby improving the performance of the heavy bio-oil.