An insert-and-twist building block structure, comprising: at least one connection bar, the connection bar having at least one end from which a combination projection section extending outward in an axial direction, the combination projection section having an outside diameter that is increased from a distal end toward a proximal end so as to form a conic shape, the combination projection section having an external circumferential surface that is formed with at least one bead ring, the bead ring including multiple raised beads that are arranged in a ring configuration in an intermittent form; and a connection terminal unit, which comprises at least one connection terminal, the connection terminal having at least one end that is recessed inward in an axial direction to form a combination cavity, the combination cavity having an inside diameter that is decreased from an outer end toward an inner end so as to form a conic shape, the combination cavity having an internal circumferential surface that is formed with at least one groove ring, the groove ring including multiple recessed grooves that are arranged in a ring configuration in an intermittent form, the recessed grooves being extended in a radial direction of the internal circumferential surface of the combination cavity and being each formed as an elongate strip, each of the recessed grooves has a middle portion that forms a deep trough section and two end portions each forming a shallow trough section, the recessed grooves each having a depth that is decreased from the deep trough section toward the shallow trough section; wherein the combination projection section of the connection bar is insertable into the combination cavity of the connection terminal to have the raised beads received in the deep trough sections of the recessed grooves to achieve combination; and the connection bar is rotatable to have the raised beads moved in a direction from the deep trough sections of the recessed grooves toward the shallow trough sections, so as to separate the connection bar and the connection terminal from each other. at least one connection bar, the connection bar having at least one end from which a combination projection section extending outward in an axial direction, the combination projection section having an outside diameter that is increased from a distal end toward a proximal end so as to form a conic shape, the combination projection section having an external circumferential surface that is formed with at least one bead ring, the bead ring including multiple raised beads that are arranged in a ring configuration in an intermittent form; and a connection terminal unit, which comprises at least one connection terminal, the connection terminal having at least one end that is recessed inward in an axial direction to form a combination cavity, the combination cavity having an inside diameter that is decreased from an outer end toward an inner end so as to form a conic shape, the combination cavity having an internal circumferential surface that is formed with at least one groove ring, the groove ring including multiple recessed grooves that are arranged in a ring configuration in an intermittent form, the recessed grooves being extended in a radial direction of the internal circumferential surface of the combination cavity and being each formed as an elongate strip, each of the recessed grooves has a middle portion that forms a deep trough section and two end portions each forming a shallow trough section, the recessed grooves each having a depth that is decreased from the deep trough section toward the shallow trough section; wherein the combination projection section of the connection bar is insertable into the combination cavity of the connection terminal to have the raised beads received in the deep trough sections of the recessed grooves to achieve combination; and the connection bar is rotatable to have the raised beads moved in a direction from the deep trough sections of the recessed grooves toward the shallow trough sections, so as to separate the connection bar and the connection terminal from each other.