The invention discloses a method for ascertaining degree of maturity of tridacna ovums. The method comprises the following steps: A, tridacna parent selection: selecting healthy and undamged individual tridacna as an ascertaining object of the degree of maturity of ovums and cleaning and temporarily rearing selected tridacna into seawater; B, collection of gonadal tissues: utilizing an injector tostretch from a tridacna water outlet hole, insert into a gonad surface-layer tissue of tridacna and absorb gonad tissue; C, ascertaining of degree of maturity: performing microscopic observation on the collected gonad tissue. Under a microscope, the observed condition of the degree of maturity of ovums comprises the following three types including an ovum-immaturity stage where ovums are shaped like teardrops or pearls and have the diameters not up to the specification of naturally-discharged ovums; an ovum-maturity stage where ovums are circular or elliptical and have the diameters identicalto ovums in sizes with yolk containing enriched accumulated matter and the ovums have double-layer smooth ovum membranes; and a ovum-maturity stage wherein ovums are circular and the ovum membranes wrinkle so that ovums are likely to crack, thereby making yolk overflow.