This study aimed to examine the learning progression (LP) model of scientific imagination among undergraduate students using the Scientific Imagination Test-Verbal (SIT-Verbal) and investigated the influence of students' demographic characteristics including gender, age, and discipline on their scientific imagination. Six hundred and sixteen undergraduates from a university in southern Taiwan participated in this study. The SIT-Verbal covered four key components of the scientific imagination process: brainstorming, association, transformation/elaboration, and conceptualization/organization/formation. The multiple validities of SIT-Verbal were assessed via a Rasch partial credit model. The results indicated that the SIT-Verbal had good model-data fit, supporting that undergraduate students' scientific imagination in four stages from brainstorming, association and transformation/elaboration to conceptualization/organization/formation. Additionally, the results showed that the SIT-Verbal was suitable for measuring students' scientific imagination at the university level. The study also provided abundant evidence verifying the SIT-Verbal and supported the learning progression for undergraduate students' scientific imagination.