Is it necessary to pass in all subjects in jee mains to get into dtu???

No. Overall marks will be count to prepare merit list. there is no subject wise cut off for DTU or JEE Main.

Qualifying marks criteria for B . E ./ B . Tech at DTU :

-Candidates need to have secured at least 60% aggregate marks in Physics, Chemistry and Mathematics at Senior School Certificate Examination Level/XII.
-They also need to have passed English as a subject (Core or Elective) at Senior School Certificate Examination Level


You did not mention your category so i am assuming General category.

To get Mechanical branch under Delhi home state quota and general category, your rank should be under 15000 in JEE Main and marks should be between 170-80 marks.

You can check category and branch wise cut off of DTU, Delhi by below link:

DTU Cut Off

Good Luck.