This paper reports the discovery of new slowly pulsating B-type stars. Based on the photometric, spectral, and astrometric data of the TESS, LAMOST, and Gaia surveys, we have found 286 new slowly pulsating B-type (SPB) stars and 21 candidates. Among these, 20 are Be stars or candidates with emission-line profiles. It is shown that these SPB stars have luminosities between 40 and 2850L_{sun}_ and effective temperatures ranging from 10000 to 21000K. Their pulsation periods are from 0.14 to 6.5d with amplitude ranges of 0.2-20mmag in the TESS band. It is indicated that these targets follow the distribution of the SPB stars in the period-luminosity and the period-temperature diagrams. Their positions on the H-R diagram reveal that most of these pulsators are distributed in the instability region of SPB stars, in the main-sequence evolutionary stage, and with mass ranges of 2.5-7M_{sun}_. However, there are some targets beyond the red edge of the theoretical instability region, which should be caused by the rapid rotation reducing the measured effective temperature. The discovery of these new SPB stars increases the total number by over 60%, which are significant samples for further investigating the structure and evolution of intermediate-mass and even massive stars by asteroseismology.