The relation between the transformation rates of photochemistry reaction and the time of illumination was described. Under the conditions of optimum matched spectrum

the ergosterol used as raw materials will beturned into vitamin-D

2

and other byproducts. By series of experiments

it is found that the 283nm-waved ultraviolet light source is fit for the photochemistry reaction.With this light source

the transform effect is best. With increasing illumination time

the transformation rate goes up and the content of the main product vitamin-D

2

increases.But at the same time the content of the by-products including tachysterol and lumisterol increase accordingly.So the time of illumination is a key factor in the production of vitamin-D

2

. We hope that these data on Vitamin D

2

will be usefal to producers

with which they can compare their manufacture parameters and improve their production technology.