Hi! Unfortunately, there is no syllabus for the USMLE Step 1 exam though we all wish there was one.
However, all the subjects that will be tested by the exam are:
- Fundamental pathology and pharmacology
- Cardiovascular system
- Endocrine system
- GI system
- Nervous system
- Renal system
- Reproductive system
- Respiratory system
All the high-yield information for USMLE Step 1 are nicely summarized in First Aid, the gold-standard book for studying for USMLE Step 1. Doing UWorld Qbank (~2500 questions) questions to familiarized yourself with Step 1 style questions is also a must!
Hope this helps and best of luck!