Abstract: Based on the measured data of spectral radiation on Qinghai Xizang Plateau from April to October, 1994, ratio of photosynthetically active radiation ( PAR ) to global radiation was presented, i.e. η =0.439±0.009, and 1J energy of PAR is equivalent to 4.43 μmol quantum. In the climatological estimation of Qinghai Xizang Plateau, following equations can be used to estimate the averages for every ten days of daily total PAR energy H_PAR（MJ·m^-2d^-1）and daily total quantum U_PAR（mol·m^-2d^-1）:H_PAR=（0.399+0.036lgE^*）·H U_PAR=（1.768+0.159lgE^*）·H H（MJ·m^-2d^-1） is the average daily global radiation for ten days. E^*=E·P₀/P,P₀（hpa） is the standard atmospheric pressure, P (hpa) is the atmospheric pressure at the spot, E (hpa) is the water vapor pressure on the ground.

Key words: Qinghai Xizang Plateau, photosynthetically active quantum value, climatological estimation