Abstract: A new type of logging transmit circuit applied to measurement while drilling （MWD） based on DDS technology is presented.As for logging instrument，electromagnetic wave source is very important.Its performance affects the whole performance of the system directly.LWD （logging while drilling） signal waveform generation circuit，peripheral signal processing circuit，DDS module，DSP and AD9850 interfaces，software design flowchart etc are given.2MHz and 400kHz digital transmit circuits mainly composed of DDS AD9850 chip，which carries out the shift of the phase and the limit of the amplitude easily，are designed and debugged successfully.it is used to substitute for the conventional transmit circuit，so the alldigital transmit channel of phase shift is achieved.The experimental result shows that the logging transmit circuit for MWD is feasible.

Key words: DDS(direct digital synthesizer), measurement while drilling, low power, electromagnetic resistivity logging, frequency stabilization