The invention discloses a downhole turbine generator used for measuring while drilling. The downhole turbine generator comprises a turbine drive unit (1), a generator unit (2) connected with the turbine drive unit (1), a brake holding device (3) installed on a rotor shaft of a motor, and an electronic control unit (4). The turbine drive unit (1) is arranged on the outer portion of a rotating shaft of the generator unit (2). When a well drilling medium passes through a blade of the turbine drive unit (1), the blade of the turbine drive unit (1) can rotate under the action of fluid, and therefore a rotor of the generator unit (2) is driven to rotate. The inclination of the blade can be changed and is used for adjusting the output voltage of the downhole turbine generator to be stable when different well drilling liquid media and well drilling liquid media with different displacements are used during measuring while drilling. The rotating speed of the rotor can be reduced by holding the rotor shaft of the generator through the brake holding device. The output voltage of the generator is collected through the electronic control part, and an instruction is sent out so as to adjust the rotating speed of the generator.