Abstract: A design and experimental research on downhole outer magnetic rotor turbine alternator was proposed to fulfill the life and power requirements of the turbine alternator in the vertical drilling system.The electrical parameters of the alternator were designed by theoretical and simulation methods,a simulation model was built to carry out electromagnetic field,field-circuit coupling and thermal field simulation,the electromagnetic characteristics,loss and temperature increments data were gained by simulation.The analysis result showed that the power output the alternator reached design targets(800 W),and the maximum stable state tempreture increments at maximum power output were 23 ℃.Then a field experiment was carried out to verify the theoretical calculation and simulation.During the experiment,the stable maximum power output reached 1 000 W,stable state tempreture increments were 20.5 ℃,after 320 h field experiment,the alternator worked normally.The research and experiment shows that the performance of downhole outer magnetic rotor turbine alternator reaches design targets,and it might be a solution to power requirements of vertical drilling system and other downhole instruments.