A cushion for improving sitting posture, comprising a cushion body (1). The cushion body (1) can be placed on a plane. At least two hump portions (11 and 13) are formed on the cushion body (1). The two hump portions (11 and 13) are a first hump portion (11) and a second hump portion (13), respectively. The first hump portion (11) and the second hump portion (13) are used for supporting the parts of a human body corresponding to the front and back of the pelvis (3), respectively. The first hump portion (11) and the second hump portion (13) are arranged at an interval, so that a trench (12) is formed on the cushion body (1) between the first hump portion (11) and the second hump portion (13). The trench (12) is used for supporting the part of the human body corresponding to the lower end of the ischium or the lower end of the sacrococcyx. The cushion can relax the hip joint and surrounding muscles of the human body so as to facilitate blood supply, can ensure that the human spine always tends to maintain a correct curve so as to protect the lumbar vertebrae (2) of the human body, and can also further relax the cervical vertebrae and surrounding neck muscle tissues so as to prevent backache and headache.