Abstract: Two kinds of metrical system of photosynthetically active radiation (PAR)were described.An equation of climatological estimating quantum flux densities was provided using by the irradiance of global radiation. Based on the measured data of spectra and the correlated colour temperature in abroad,a coefficient converting PAR energy into quantum was presented,i.e.l J energy of global radiation in photosynthetically active spectrum is equivalent to 4.55 μcmol quantum.In climatological estimation a conversion between the two kinds of metrical system,quantum and energy of PAR can be carried out for climatological estimation.