Background Childbirth preparation plays an important role in reducing maternal mortality and improving women's childbirth experience. Evaluating childbirth readiness levels before and after interventions provides a basis for formulating more targeted and effective interventions. However, existing tools only assess partial childbirth preparation or have limited evidence of reliability and validity. The aim of this study was thus to develop a new instrument for use during the third trimester to comprehensively assess the readiness level of pregnant women, and test the scale's psychometric properties. Methods The scale was developed through exploratory mixed methods including qualitative and quantitative phases. A literature review and in-depth semi-structured interviews were utilized to identify the scale items. A Delphi expert consultation evaluated the content validity. Psychometric testing was conducted in a convenience sample of 731 pregnant women in the third trimester (recruited from 3 tertiary hospitals in Hubei province in China). Item analysis was used to screen items; exploratory factor analysis was performed to extract factors; confirmatory factor analysis was performed to evaluate fit on the factor structures. Results The final scale consisted of four dimensions and 18 items that explained 65.8% of the total variance. Confirmative factor analysis (CFA) model showed that the 4-factor model fits the data well. The total Cronbach alpha coefficient of the total scale and 4 factors was 0.935 and 0.853-0.914. The split-half reliability was 0.880. The dimensions comprised "Self-management", "Information literacy", "Birth confidence" and "Birth plan". Conclusions The childbirth readiness scale we developed has good reliability and validity, and can be used to comprehensively assess the readiness level of pregnant women. In addition to understanding the overall level of women's childbirth readiness, using subscale scores, improvements can be targeted to specific areas of the preparation for childbirth, to improve the efficiency of the intervention.