A flexible surgical instrument has structural backbones in crossed arrangement, the flexible surgical instrument includes a flexible continuum structure comprising a distal structure, a proximal structure and a middle connection body; the distal structure includes a first distal segment and a second distal segment, the proximal structure includes a proximal segment; first segment structural backbone(s) on the proximal segment and first segment structural backbone(s) on the first distal segment are fixedly connected respectively one to one or are of the same structural backbone; second segment structural backbone(s) on the proximal segment and second segment structural backbone(s) the second distal segment are fixedly connected respectively one to one or are of the same structural backbone; the middle connection body includes two passage fixing plates, between which structural backbone guiding passage(s) and structural backbone cross guiding passage(s) are fixedly connected; the first segment structural backbone(s) (163, 123) extends through the structural backbone cross guiding passage(s) (153), the second segment structural backbone(s) extends through the structural backbone guiding passage(s).