Meniscus dynamic behaviors, as well as its optimal waveform of driving signal, in a squeeze mode piezoelectric inkjet device are studied in this paper. To use the squeeze mode piezoelectric inkjet device as a drop-on-demand dispenser, the driving signal is trapezium waveform. The parameters in a trapezium waveform of the driving signal include rise time (trise), dwelling time (tdwell), fall time (tfall) and voltage (Vp). Among these parameters, the most important parameter of driving signal is the dwelling time. To demonstrate the importance of dwelling time, a LED signal synchronized with the driving signal is used to visualize the instantaneous meniscus shape under a microscope. Experimental results show the meniscus oscillation at beginning and droplet ejection at the later phase. It is found there is an optimal dwelling time. At the optimal dwelling time, droplet ejects in a minimum time and its ejection velocity reaches the maximum. The optimal dwelling time can be further identified it relates to a pressure wave oscillation within the device. The optimal dwelling time can be approximated as the length (L) of the piezoelectric inkjet device divide by the speed of sound (c) in the dispensed fluid.