To clarify the side effect of multi-bubble cavitation at pre-focus and post-focus in high intensity focused ultrasound (HIFU) treatment and further optimize HIFU treatment, this paper records the spatial distribution of multi-bubble and multi-bubble sonoluminescence (MBSL) at different acoustic intensities in the focused ultrasound field mediated with degassed water using high-speed camera system and digital camera, respectively. Besides, the cavitation characteristics of multiple bubbles and the overall luminous intensity of sound field are separately detected by passive cavitation detection (PCD) technology and photomultiplier tube (PMT) system. It is found that when acoustic intensity is low (such as 3 047 W/cm²), bubbles distribute as a typical standing wave pattern. With the increase of acoustic intensity, a cluster of bubbles gathers at focus, then grows towards post-focus, and 3-6 MHz broadband emissions increase monotonically. Moreover, MBSL firstly occurrs pre-focus and is enlarged towards the surface of the transducer, and the overall luminous intensity of the sound field is proportional to acoustic intensity. When acoustic intensity is sufficient (such as 21 328 W/cm²), the cavitation bubbles at focus collapse tempestuously with a continuous hiss, and an elliptical bright spot appears at focus. The accumulation of bubbles sharply weaken the overall luminous intensity of the sound field.