The 150kV bouncer modulator is designed to drive the 10MW multi-beam klystron for the DESY TESLA Test Facility. The modulator is different from the 10kV modulators previously built at Fermilab. First, the new 150kV bouncer modulator has no transformer, so the modulator circuit is simplified and the output waveform is improved well. Second, the bouncer circuit has been changed to fit the output need, which is the most significant challenge. This paper gives the design of the 150kV long pulse bouncer modulator.