This paper presents the development and analysis of a longitudinal-radial composite spherical shell ultrasonic transducer, designed to address the need for omnidirectional and extensive ultrasonic radiating areas in ultrasonic applications. The transducer comprised of a sandwich piezoelectric converter, a stepped horn, and a metal spherical shell. The longitudinal vibration of the sandwich piezoelectric converter and the stepped horn excites the radial vibration of the metal spherical shell, thereby enabling omnidirectional ultrasonic radiation along the exterior of the spherical shell. Theoretical analysis was conducted using electromechanical equivalent circuits derived for both the metal spherical shell and the composite transducer. Numerical simulations were employed to investigate the vibrational characteristics, including the displacement distribution and resonance frequency. The transducer was subsequently designed and fabricated, with experimental measurements performed to evaluate its vibration characteristics and radiated acoustic field. The experimental results demonstrate good consistency with both analytical predictions and numerical simulations, confirming the transducer's capacity for use in ultrasonic technology requiring extensive radiating surfaces.