The invention discloses a horizontal excitation test device, a combination thereof and an installation method of the device. The horizontal excitation test device comprises a vibration exciter fixed on the ground, a decoupling mechanism is arranged on the vibration exciter, a hoop device is arranged on the decoupling mechanism, the vibration exciter transmits power to the hoop device, a hanging device is arranged on the hoop device, the hoop device is hung by the hanging device, a lifting supporting device is arranged below the hoop device, and the hoop device is supported by the lifting supporting device. Synchronous or asynchronous parallel excitation of the vibration exciter on the test piece is realized by adopting the decoupling mechanism; the hanging mechanism is arranged to hang the clamping mechanism so as to balance the gravity of the test piece; a plurality of vibration exciters are arranged, so that the horizontal multipoint synchronous or asynchronous vibration test of a long test piece can be completed, the eccentric moment resistance is very large, and the horizontal parallel excitation test of large size, large mass and large scale can be met.