The invention provides a double-direction precise hydraulic bar shearing machine and a shearing method of the machine. At the beginning of shearing, a moon arc notch is cut in the radial left side of a bar, a gap is cut in the hard layer of the radial surface, stress concentration and slight bar lattice slippage are generated, a shear switch issues an order to an oil cylinder immediately, the motion direction is reversed to the leftward movement, a rear cutter shears off the bar along the gap, and for example, when low-carbon steel is shorn, the radial pressure skewness is small, and burrs are few; and if high-carbon alloy steel is shorn, the center portion cannot be torn off. The double-direction precise hydraulic bar shearing machine comprises a sliding block, a front cutter portion, a rear cutter portion, a shear depth adjusting portion and a spring device. The front cutter portion is used for centering and clamping the bar and is mounted on a front lathe, and the front cutter portion comprises a left wedge, a left cutter table, an oil cylinder, a right wedge, a right cutter table, a screw and blades.