To describe and analyze the distribution and trends of pre-pregnancy body mass index (BMI) among reproductive-aged women with pregnancy intention in Gansu province. Methods: A total of 1 009 906 women who participated in the National Free Pre-pregnancy Checkups Project in Gansu province during 20132019 was included. Annual crude and age-adjusted BMI means and underweight, overweight, and obesity prevalence of these women were calculated. Simple linear regression model, generalized linear regression model, and logistics regression model were used to get the annual trends of BMI means and BMI categories prevalence. Annual trends according to baseline characteristics were also calculated. The difference rate of BMI annual growth was compared among the women with different characteristic. Results: The standardized BMI had increased from 21.39 kg/m2 (95%CI 21.36-21.42) in 2013 to 21.91 kg/m2 (95%CI 21.89-21.93) in 2013 (P<0.001), with an annual increase of BMI by 0.09 (95%CI 0.07-0.10) kg/m2 after multifactor adjustment. The standardized obesity rate has increased from 1.86% (95%CI 1.66%-2.08%) in 2013 to 3.25% (95%CI 3.10%-3.41%) in 2019 with an annual increase of obesity by 14.32% (13.37%15.27%) kg/m2 after multifactor adjustment. And the increasing trend of BMI and obesity prevalence of the women in Hexi region of Gansu was faster than which of the women in southeast Gansu. The BMI and obesity prevalence of the women aged 20 to 25 years, the women with senior high school education level or above, the women worker, and the women lived in cities of per capita GDP >70 000 Yuan had showed faster increasing trend. Conclusion: the prepregnancy BMI value and the obesity prevalence of the women with pregnancy planning is increasing in Gansu province. And public health authorities should strengthen the awareness of the preconception obesity epidemic, and should take more effective strategies to control the pre-pregnancy obesity.