Background: As an important tumor marker for follow-up and prognosis of ovarian cancer, CA125 is not suitable as a screening indicator due to its frequent elevation in many physiological or pathological condition, thus women are often puzzled by unaccountably elevated levels of CA125. While we have known that the CA125 level is differed by age and benign gynecological diseases, the specific trend of CA125 level changes is still not clear. We hope that this study will contribute to a more accurate and individual interpretation of CA125 by evaluating the baseline levels of CA125 in healthy women of different ages and analysis the association between benign gynecological diseases and CA125 level. Methods: This was a cross-sectional study enrolled 73390 women without ovarian cancer from January 2016 to December 2021 in three health examination centers. We have assessed the distribution of CA125 levels in different age groups and analyzed the variation trend of CA125 levels by age among women with normal ultrasonic results, as well as performed the correlation analysis between several benign gynecological diseases and CA125 levels. Results: 55422 women with normal ultrasonic results and CA125 level <200U/mL were included in the analysis of variations in CA125 depending on age. We observed CA125 levels were linearly associated with age (R²=0.0503, p<0.0001). Using the group <30 years as a baseline, average CA125 levels decreased by 3.4%, 10.1%, 42.6%, 40.5%, 31.8%, and 20.3% by every 10 years. With the increase of age, the downward trend of CA125 began to reverse at the age of 60, and it showed significantly difference between each adjacent subgroup (p<0.05). 8630 women were selected with abnormal ultrasonic results, we observed that CA125 was lower in women with uterine effusion, higher in endometrial hyperplasia, endometrial polyps, hydrosalpinx, ovarian cyst, adenomyosis and uterine fibroids. Age and all those diseases demonstrated possible associations (p<0.05) with CA125 levels ≥35U/ml in univariable logistic regressions. Multivariable analysis identified that ovarian cyst (p<0.001), adenomyosis (p<0.001) and uterine fibroids (p=0.018) were still significantly associated with abnormal CA125 level. Conclusions: With the increase of age, CA125 level generally showed a downward trend, but there is a slight increase in CA125 after age 60. Ovarian cyst, adenomyosis and uterine fibroids demonstrated significant associations with abnormal CA125 level.