The invention discloses a fragile transverse plane grinding machine used for a rock test. The fragile transverse plane grinding machine comprises a pedestal, a workbench mechanism, an actuating mechanism and a clamping mechanism, a workbench is connected with the pedestal through an elastic component and is limited to a press height by a stop block, sand paper is arranged on the workbench, the actuating mechanism uses a crank slide block principle to realize linear repetitive motion from motor rotation to a guide rod, the clamping mechanism is connected with the guide rod for clamping a rock sample, the rock sample is driven by the motion mechanism, the bottom performs reciprocating motion on the sand paper, and thereby polishing is realized. The grinding machine realizes the stable contact of the rock sample and the sand paper as well as automatic grinding, requirement of rock mechanics test on the extremely fragile rock sample can be satisfied, rate of section edge damage of the rock sample is reduced, and a traditional form of preparation of the fragile rock by artificial operation can be avoided. The structure is simple, the application of the grinding machine is convenient, and the grinding machine is convenient for popularization to the field of the preparation of the rock sample used for indoor rock mechanics test.