Radio observational results at 232 MHz and multifrequency studies of the supernova remnant (SNR) HB21 are presented. Its integrated flux density at 232 MHz is about 390 ± 30 Jy. Both the integrated spectral index and the spatial variations of spectral index of the remnant were calculated by combining the new map at 232 MHz with previously published maps made at 408, 1420, 2695, and 4750 MHz. The SNR has an integrated spectral index of about α=-0.43 (Sv ∝Vα) between 232 and 4750MHz. In general the spectral index varies from-0.5 in southeast and west regions of the remnant to-0.3 in the central region and near the northwest edge. The new data of 232 MHz reveal that there is interaction between the remnant and the surrounding gas along the east edge of the remnant which causes the spectrum flattening at low frequency, while the very good agreement between the structure of X-ray emission and the central flat spectrum area suggests that the existence of thermal emission is the reason of spectrum flattening in thearea.