The utility model discloses a sealing test checking device for a mobile crane, which comprises the components of: a dial gauge, a base which is used for fixing the dial gauge and is mounted on a derricking cylinder, and an elongated pole which is longitudinally arranged and has a lower end that contacts with a measuring pin of the dial gauge. The elongated pole is mounted on the piston cylinder through other bases arranged on the upper end of the elongated pole. The base for fixing the dial gauge is a third magnetic base. After the dial gauge is fixed, the base is attracted to the derricking cylinder through magnetism of the base. Two other bases are arranged on the upper end of the elongated pole, namely a first magnetic base and a second magnetic base. After the first magnetic base and the second magnetic base are connected with and fixed with the elongated pole, the first magnetic base and the second magnetic base are attracted on piston cylinder through magnetism themselves. The sealing test checking device provided by the utility model has functions of: realizing quick mounting and number reading of an instrument in the sealing test checking process, and reducing danger in climbing operation. Furthermore the sealing test checking device has advantages of: simple process, reliable performance and low cost.