Balance arm and tower crane

The invention provides a balance arm and a tower crane. The balance arm comprises an arm body and a shielding portion, a balancing weight installing port is disposed on the arm body, the shielding portion is used for adjusting the size of the balancing weight installing port, and the shielding portion is installed on the arm body and capable of moving relative to the arm body. According to the balance arm and the tower crane, when a balancing weight or all balancing weights is/are not required to be installed, an open portion of the balancing weight installing port on the arm body can be covered at any time through the shielding portion, so that the potential safety hazard is eliminated, and the safety is improved. Besides, an installation platform is not required to be arranged on two sides of the arm body, so that the cost is lowered.