To analyze the expansion characteristics of pulsed plasma jet in air, the expansion process of pulsed plasma jet generated by a plasma generator was studied by a piezoelectric pressure sensor and a digital high-speed video system. The relation of change in the extended volume, axial displacement and radial displacement of pulsed plasma jet in atmosphere with time under different discharge voltage and jet breaking pressure was treated and obtained by Photoshop software. Results show that when the pulsed plasma jet is expanded, its shape is gradually extended from the initial shape like ellipsoid to a conical head and an elongated cylindrical tail. The axial displacement of the jet is always larger than the radial displacement. Extended volume reveals a single peak distribution with time. Increasing the discharge voltage and jet breaking pressure can improve the expansion ability of the jet, and the larger the discharge voltage, the more violent the turbulent mixing in the plasma jet expansion.