The invention provides a radar speed measuring instrument applied to a tunnel and provided with a rapid mounting support. The radar speed measuring instrument comprises a first piston rod, a pipeline,a second piston rod, a clamping rod, a conical block, a base, a mounting seat and a sleeve, the first piston rod is installed on the upper side in the pipeline through a micro spring, the right end of the first piston rod penetrates through a positioning rod to extend into the clamping rod, the pipeline is arranged in the base, the second piston rod is installed on the lower side in the pipelinethrough a second micro spring, the clamping rod is fixed on the portion, on the right side of the positioning rod, of lower end face of the mounting seat through a screw, the lower end of the clampingrod extends into the base, the conical block is fixed at the portion, on the right side of the clamping rod, of the lower end of the mounting seat through a screw, the lower end of the conical blockextends into the base, the conical block is attached to the second piston rod, and the sleeve is arranged on the annular side surface of the fixing column. Through the design, the use is convenient, assembling and disassembling are facilitated, moreover, the fixing effect is good, and height and direction can be conveniently adjusted.