Based on a spherically symmetric bubble model, the threshold shear stress for H-22 cells which are irradiated by continuous focused ultrasound is estimated. On the condition that the final concentration of the superparamagnetic iron oxide (SPIO) in the cell suspension is 410 g/mL, the focused ultrasound sonication is at a frequency of 1.37 MHz, the power from amplifer is 2 W, and H-22 cells are exposed to the ultrasound for 60 s, the labeling efficiency is about 45.9%13.5%. Prussian blue staining confirms iron uptake and shows numerous blue-stained iron particles in the cytoplasm, while more than 90% labeled cells remained viable. The results show that the reparable sonoporation arises in plasma membrane and SPIO nanoparticles enter into the H-22 cells. Numerical calculations show that the shear stress acting on the cell is 697 Pa, which is the threshold shear stress for H-22 cell sonoporation.