What is the minimum mark for getting pass in Aipmt preliminary exam???

It is not just sufficient to Pass. You need to come in the merit list. And for this it is essential to get more than 50% marks. However the percentage gets increased every year and the merit depends on other factors also such as number of candidates and number of medical seats.

you need to get minimum 320 marks or more & in mains more than 50% in each subject to persuing MBBS degree