The utility model provides a NVH test of adjustable length is with propping cover belongs to automotive test instrument technical field. It has solved set commonality subalternation technical problem that props in the current car NVH test. Originally, prop the cover including all being the cylindrical cover body no. 1 and the cover body no. 2, have the internal thread in the cover body no. 1 on the inside wall of the connecting hole and the cover body no. 1 is offered to a cover body axial, have the external screw thread on the outer peripheral face of the cover body no. 2, the one end of the cover body no. 2 insert establish in the connecting hole of set body no. 1 and the internal thread outside with thread to match close and be connected. The utility model discloses in the cover body no. 1 through setting up the looks spiro union constitute with the cover body no. 2 and originally prop the cover, only need use during the use spanner rotary sleeve body once or two covers that prop that can obtain different length of the cover body, the spanner that not only facilitates the use of the planar structure on the cover body no. 1 or the cover body no. 2 simultaneously, make things convenient for moreover in the process of the test power hammer strike with the pasting of accelerometer.