We demonstrated the arbitrary pulse shaping for a high power, joules class, and multi-pass ring Nd: glass laser amplifier system with nanosecond pulses based on the direct calculation method. While the square pulse with pulse energy 0.9mj and FWHM (full width at half maximum) pulse width 6ns, a 0.9J at 1Hz high power laser pulse energy is generated, which has the ability to change the waveform arbitrarily based on the full fiber front end. The laser amplifier system consists of three parts: full fiber seeder, diode pumped Nd: glass regenerative amplifier, and multi-pass ring amplifier. With the help of direct calculation method based on the input-output model, the input pulse shape has been calculated and the output pulse shape has been compared to the target pulse shape, showing that the simulation and experiment is consistent. Some other interesting pulse shapes have been produced with pre-compensated inject pulse based on the calculation which shows great potential to be applied in high power laser amplifier system with a desired pulse shape.