The cytology of the fertilization and early embryonic development of Tegillarca granosa were consecutively observed by optical microscope and paraffin section method.The unfertilized mature eggs were at metaprophase of first meiosis;After mixing of sperms and eggs,sperms quickly attached to the surface of the egg,and the maturation division began;At about 9-12 min and 18-20 min,the fertilized eggs released the first and the second polar bodies respectively in the progress of maturation division;After completion of second maturation division,at about the 20 min,sperm nucleus and the haploid female nucleus expanded immediately and developed into the male and female pronuclei,and the male pronucleus formed earlier than the female pronucleus;At about 25 min,the two pronuclei combined and their chromosomes formed respectively;At about 35 min,the chromosomes were separated equally into two daughter cells which are different evidently in size;At about 45 min,the second cleavage was completed with the result of forming four daughter cells,one big and three small.Additionally,polyspermy were observed in the experiment,and several male pronuclei can combine with the female pronucleus and form polyspindles.The reasons of polyspermy and results of embryonic development of Tegillarca granosa were also discussed deeply.