The invention provides an automatic contact instrument used for measuring thin sheet material dimensions. The automatic contact instrument comprises a measuring head, a control system comprising a numerical control and calculation module, and a shaft system moving along a three-dimensional coordinate, wherein the measuring head comprises a guide rail die and a guide core, the guide core penetrates through the guide rail die, the guide rail die has an air inlet and an air guide groove, an air guide rail is formed in the guide rail die, a top portion of the guide rail is provided with the air inlet, a bottom portion of the guide rail is connected with a spring, the spring is arranged between the guide core and a bottom board, a lower end of the spring is connected with a probe, a top portion of the guide core is connected with a raster ruler, the raster ruler is connected with a laser displacement sensor, and the laser displacement sensor is connected with the control system. The measuring head of the measuring instrument employs the pneumatic control technology, precise adjustment on a measuring force can be realized through changing internal and external air pressure of the guide core, a value of the measuring force can be not only adjusted, but also the measuring force is guaranteed to be constant; a three-dimensional motion platform is employed in combination with the numerical control technology, all-round and automatic measurement is realized, and thereby measurement precision of surface dimensions of thin sheet material type elements can be improved.