Raina's century was the only bright spot in a gloomy trip to the west country for India, who struggled with bat and ball and also allowed England Test captain Andrew Strauss to rediscover his form with scores of 78 and 109.
The Indians had been completely out-played by Somerset on the first two days of this three-day match and started Sunday's play on 138-8 after allowing the hosts to amass 425-3 declared in their first innings.
India's battling line-up had been demolished by South African left-arm seamer Charl Willoughby, who took 5-50 on Saturday as the likes of Sachin Tendulkar and Rahul Dravid failed to deliver.
Willoughby quickly claimed his sixth wicket on Sunday as he bowled Sreesanth, but Raina, who began the day on 30, cut loose after that to restore some pride for the tourists.
The 24-year-old added 84 for the final wicket in an explosive 12-over partnership with Munaf Patel, who contributed just six as Raina hit 15 fours and five sixes to reach 103 in 112 balls.
Raina's innings underlined his case to start against England at Lord's in the first Test on Thursday and he may have caused even more carnage if Patel had not fallen lbw to leg-spinner Max Waller with the score on 224.
India's bowlers had struggled to adapt to English conditions on the flat Taunton track in the first innings and it was more of the same as Somerset opted against enforcing the follow-on.
Zaheer Khan and Tendulkar did not take the field, but Indian officials played down any injury fears by insisting the duo were were just resting.
In their absence, Middlesex opener Strauss, guesting for Somerset to get some much-needed practice, underlined his return to form as he recorded an unbeaten 109 including 18 fours.
To add insult to injury for India, Peter Trego's 85 not out included a brutal demolotion of Amit Mishra, who at one stage bowled three overs for 61, and piled on the misery for an attack missing the rested Ishant Sharma and Harbhajan Singh.
Somerset eventually declared on 260-2 and India at least managed to avoid any further problems as openers Gautam Gambhir and Abhinav Mukund reached 69-0 before the match was declared a draw.
Copyright AFP (Agence France-Presse), 2011