The share of station of hydraulic pressure power of numerical control lathe can regard park of a module as the machine tool from the back. When the big lot that needs to use tailstock center is machined, can add system of tip of tailstock of outfit hydraulic pressure, make become another to be able to operate module, system of power of common and same hydraulic pressure. In treatment, when the program moves to need to have gearshift state, numerical control system gives out shutdown alarm first, next the program gives out control signal to make hydraulic pump starts for oil, at the same time the electromagnetism a powerful person of hydraulic pressure system undertakes suction closing according to controlling signal, offer oil to gearshift oil cylinder, make piston lever is extended or go back, drive batch of fork to make gear has speed change, after gear shift reachs the designated position, cam touchs micro-gap switch, feedback signal comes numerical control system, criterion gearshift ends, the program continues to run executive treatment workpiece downward. Installation of module of main shaft gearshift is on main shaft box, its wait for composition by bracket, oil cylinder and vitta, micro-gap switch. Bracket grows broad measure and measure of department of main shaft roof identical, installation of module of gearshift of whole main shaft is in above main shaft box on the 4 bolt opening that is used at installing cover board to use formerly, add dozen of fixed position to sell the opening fixed position with making module. Bracket is mid clapboard is propped up, gearshift oil cylinder is fixed go up in clapboard, the tine axle that is located in place to want to control slippage upper part, with oriented axis coaxial; Lever of oil cylinder piston is located in inside oriented axis, dial fork to pass bearing pin connection with gearshift; Gearshift dials fork to cover go up in oriented axis, can be in of piston lever drive next edges to direct the axis moves back and forth; Oriented axis is hollow leave have oriented chamfer, so that piston lever and gearshift move forked link, oriented axis is secured by bearing pin go up in bracket; Two gear change dial fork to all be be down perpendicular structure, inside the gearshift groove that blocks the slippage gear in correspondence respectively. The oil cylinder when gearshift offers oil, criterion piston lever drives slippage to dial gear of forked mobile slippage through bearing pin, make gear undertakes gearshift clench the teeth, the by what dial fork to go up protruding piece touchs cover board to go up micro-gap switch after gear reachs the designated position, give out tine to be turn for a signal, end for gearshift.