A
sextant high in horizontal stability comprises a panel, a moving mirror, a fixed mirror, a
telescope, a swing arm, a mounting shell, a support, a
first light-reflecting mirror and a second light-reflecting mirror, wherein the mounting shell is a hemispherical shell with an upward end opening, a dial of the panel faces downward and is arranged in the mounting shell vertically, and the sidewall of the mounting shell is provided with a through hole allowing the fixed mirror to
expose. The mounting shell is mounted on the support by enabling the end opening thereof to keep parallel to the
sea level constantly through a rotating mechanism. The
first light-reflecting mirror and the second light-reflecting mirror are arranged on the panel, the
first light-reflecting mirror is used for receiving rays reflected by the fixed mirror and reflecting the received rays to the second light-reflecting mirror, and the
telescope is arranged on the mounting shell and capable of receiving rays reflected by the second light-reflecting mirror. The
sextant high in horizontal stability has the advantages that the mounting shell is matched with the support to enable an observation surface of the
sextant to keep horizontal to the
sea level constantly, so that horizontal stability of the sextant is improved; the first light-reflecting mirror and the second light-reflecting mirror are matched with the moving mirror and the fixed mirror to enable the reflected rays to be positioned above the mounting shell, so that observation of the rays by the
telescope is facilitated, and convenience in use is achieved.