A locking device (30), a supporting arm of the locking device and an ultrasonic imaging system. The locking device (30) comprises: a fixing base (31), a guide rod (32), a locking element (35), and a driving component. The fixing base (31) is provided with a through hole (312) penetrating through the fixing base (31)； a sliding groove (311) is further arranged in the fixing base (31) and intersects with the through hole (312). An external thread area is arranged on at least one part of external surfaces； the guide rod (32) penetrates through the through hole (312), and the external thread area is located at a location where the through hole (312) intersects with the sliding groove (311). The locking element (35) is accommodated in the sliding groove (311), a locking thread area is arranged on one end of the guide rod (32) towards the locking element (35) and may mesh with the external thread area of the guide rod (32). The driving component drives the locking element to approach or leave the guide rod (32) in the sliding groove (311). The foregoing locking device (30) locks the guide rod (32) by threads in the locking thread area meshing with external threads in the external thread area, which is simple in structure, convenient to maintenance, low in costs, difficult to lose efficacy, high in reliability, convenient to operate, and capable of bearing heavy loads. The locking device is operated without power and noise.L'invention concerne un dispositif de verrouillage (30), un bras de support du dispositif de verrouillage et un système d'imagerie par ultrasons. Le dispositif de verrouillage (30) comprend: une base de fixation (31), une tige de guidage (32), un élément de verrouillage (35), et un composant d'entraînement. La base de fixation (31) comporte un trou traversant (312) qui pénètre à travers la base de fixation (31)； une rainure de coulissement (311) est en outre formée dans la base de fixation (31) et coupe le trou traversant (312). Une région de filet exter
