After Dheeraj Jadhav's 194 and Tarjinder Singh 99 on the second day, Niraj Patel (66) and Gokul Sharma (70 not out) helped Assam pile up the huge total.
In response, Tripura were 159 for three after Samrat Singha (57 batting) and K B Pawan (51) struck important half centuries.
For Assam, Arup Das picked up two wickets in his 18 overs.
Assam: 521/5 declared.
Tripura: 136 and 159/3 in 69 overs (Samrat Singha (57 batting, K B Pawan 51, Arup Das 2/57).
