The invention discloses a precision control device for the phase delay angle of an optical fiber lambda/4 wave plate and a control method thereof and belongs to the technical field of optical fiber sensors. The device is formed by connecting a micrometer on a body of the conventional optical fiber cutting knife through a guide rail table, a guide rail and a clamping groove platform. The control method is used for strictly controlling the length of the wave plate on the basis of the precision control device and comprises the steps of: firstly adjusting the micrometer to be at a first fixed position; mounting optical fiber fixtures, respectively cutting a polarization maintaining delay optical cable and polarization maintaining optical fibers for manufacturing the lambda/4 wave plate and carrying out countershaft welding by an angle of 45 degrees after the cutting; mounting the optical fiber fixture which are at the position where the polarization maintaining delay optical cable is positioned on a fixture clamping groove and adjusting the micrometer to be at a second fixed position; and welding with low birefringence sensing optical fibers after the cutting so as to obtain the optical fiber lambda/4 wave plate. By means of the precision control device provided by the invention, the resolution ratio of the manufactured optical fiber lambda/4 wave plate is up to 10 micrometers; the length and the phase delay angle of the wave plate can be precisely controlled; and the precision requirement on the self temperature compensation of a 0.2s-grade optical fiber current transducer is satisfied.