hello anyone...

may i know why we used UHF band for walkie-talkie or also known as hand-held radio?

Hya Lee
Basically a trade-off was decided between available spectrum vs technology cost 20 years ago, plus the cross-over point between antenna size and losses like building wall materials, wet leaves on trees etc.
Also 10-20 years ago the band-width per channel needed only to support a single 2-way voice call, so little spectrum was needed per call.
UHF offered a good compromise between the conflicting factors. Antenna size can be small, losses through building materials is only around 10 dB or so, and pipework within buildings ensured re-radiation was possible within a building in UHF. Adequate transmitter power and low receiver noise factors could be achieved at low cost and high repeatability in MMICs at UHF. All this implied a good economic cell radius per base station, so UHF represented the cross-over spectrum where all the conflicting factors for mobile telephones met.
Today there is inevitably a shift towards higher frequencies (L and C band) as technology costs fall, MMICs improve and band-width demand rises.