The invention relates to a nano magnetofluid 
fracturing fluid imbibition oil-increasing method for a tight reservoir and modified nano magnetic particles. The nano magnetofluid 
fracturing fluid imbibition oil-increasing method comprises the steps that magnetic fracturing prepad fluid is pumped into a formation, a crack is formed in the formation, a 
magnetic field is applied to the well bottom, andthe modified nano magnetic particles in the magnetic fracturing prepad fluid are delivered to a target oil reservoir; a 
fracturing fluid base fluid and a propping agent for fracturing are mixed to form sand-carrying fluid to be pumped into the crack formed in the formation, so as to support the geometrical shape of the crack; and after fracturing construction, the 
magnetic field is applied to thewell bottom, thus the nano magnetic particles adsorbing 
crude oil flow back into a 
wellbore and then recovered out of the ground, and the magnetic particles are recovered through the magnetic force effect. The nano magnetofluid fracturing fluid 
imbibition oil-increasing method for the tight reservoir and the modified nano magnetic particles are suitable for an oilfield with the 
high water content, the modified nano magnetic particles have high 
lipophilicity and hydrophobicity, thus the magnetic particles adsorb the 
crude oil in the target oil reservoir and flow back to the 
wellbore through the 
pressure difference at the well bottom and the effect of the externally applied 
magnetic field, the 
crude oil output can be well increased, 
water production is reduced, the 
magnetic nanoparticles are recovered out of the ground in the oil 
recovery process, and the magnetic particles can be recovered through magnetic force to be reused, so that the production cost is reduced.