Endometrial thickness of 0.55cm is normal if it is this thick after menstruation has cleared. If the endometrium is only 0.55cm during ovulation, it is abnormal. The endometrium should gradually thicken during the ovulation period, which is conducive to the implantation of the fertilized egg, and the endometrium should reach at least 0.9cm during the ovulation period, which is a normal phenomenon. If the thickness of endometrium is only 0.55cm during ovulation or premenstrual period, it is necessary to do further examination to understand the causes of endometrial thinning, to understand the ovarian function, to understand the estrogen, and to exclude the thinning of the endometrium caused by the uterine cavity adhesion, combined with the clinical history, and combined with the laboratory examination to analyze the comprehensive analysis, and then give treatment.