Abstract: This paper deals with 118 samples of limemicrtescanning electron micro-scope (SEM) is mainly used on studying the structure of ultrafossils in limemicrete, the diameter of ultrafossils discovered in limemicrite is about 5-30μ the shapes can be described as walnut, regular round and ellipes, irregular round and ellipse, bottle, sowl, star, gear, whell, flower shape, etc.. In the last decade the ultrafossil plates were established from the period of Jurassic.This paper mainly studies on the old stratum prior to Jurassic.At present, however there is no standard fossil plate available for reference, so problematical ultrafossils are advanced for the discussion. In addition, the structures visible in the thin section and relative to the activity of algae life are analyseed. It is one of the basis by which the biogenie micrograin of limemicrite is ascertained. Three geneses of limemicrite can be observed under SEM., as follows:chemogenic, mechanogenic and biogenic. They are distinguished one from another according to their structures. It is suggested that a genetic prefix should be added to limemicrite, that means on the basis of the structure nomenclature of limemicrite/grain content to add a genetic nomenclature.