A theoretical prolate spheroid liquid model is applied to predict the target strength (TS) of krill. Scattering patterns are shown to demonstrate orientation dependence of krill TS. Length-to- wavelength ratio (L/λ) dependencies of reduced (normalized by body length squared) target strength are shown for some orientation distributions. The results can explain well-organized experimental results. The variability of the TS of krill is large where L/λ is larger than unity. Therefore, a frequency around 70 kHz is superior to 120 kHz which are ordinarily used for krill surveys.