The invention belongs to a construction technique of a railway and a road tunnel, and provides a construction technique for cutting and splitting rectangle grooves of a railway and a road tunnel. The construction technique comprises the following construction steps: setting out construction survey and determining splits 13 on the two sides of an excavated face; cutting the designed splits 13 on the two sides; cutting a rock mass 3 at a knife dropping speed of 3cm/min or by controlling the operation current of a cutter within 50-65A by means of friction force between an alloy tool bit 7 and a rock face; splitting off the rock mass 3 between the two splits; striking a split hole 14 vertical to a cut wall rock face needed to be taken out; and splitting the rock mass 3 with a splitter 3 and then taking out the cracked rock mass by utilizing an excavator or a hydraulic hammer. Construction difficulty of a drilling and blasting method is resolved substantially by adopting the construction technique of the invention; overexcavation is better controlled so that cost is effectively controlled, and the safety during construction is ensured; splitting can be finished within a plurality of seconds after cutting; and the construction technique of the railway and the road tunnel is high in operation efficiency, accurate in split size, simple in operation and convenient in maintenance.