[en] Results are presented of studies and tuning of the magnetic field of the JINR synchrophasotron over a period of 1960-74. These studies have been performed to increase the beam capture in the acceleration mode for fields 160 and 230 Hauss and to decrease its losses while accelerating. The operating level of field inhomogeneity index is chosen (n=0.65) and it is proved experimentally that this value is optimal. Using the experimental data, the amplitude and position of a first harmonic of beam orbit distortion on the radius and vertical were calculated. An optimal correction was made at the initial stage of acceleration. This decreased the beam orbit distortion from 12-16 cm down to 5-9 cm on the radius and from 11-14 cm to 1-2.5 cm on the vertical. It is shown that the tuning of the magnetic field resulted in a significant increase of the accelerated beam intensity