Sample deposition based on micro-droplet ejection has broad application prospects in the field of biomedicine. For biological cell printing, a hybrid pneumatic-electrohydrodynamic (HPEHD) micro-droplet ejection system is built in the laboratory. Strong electric field is established by applying a high voltage between the nozzle and a collector electrode. A solenoid valve is opened temporarily; high pressure gas enters the liquid storage chamber, and produces pressure pulse, which extrudes the liquid slightly from the nozzle. The liquid is further deformed in the electric field into a cone shape (Taylor cone), and then the end of the Taylor cone breaks to form a micro-droplet. The ejection process is studied using machine-vision and image processing. With Sodium Alginate (1.0%) containing human peripheral blood mononuclear cells (PBMC) as bioink, single droplet per ejection is realized, and the droplet size is reduced by 50% due to the presence of the electric field. Through flow cytometry and microscopic photos, the effect of ejection process on the short-Term viability of cells is shown to be negligible, suggesting HPEHD ejection a potential technology option for cell printing. © 2019 Association for Computing Machinery.