The defending champions posted an impressive 225 in their innings with Trent Johnston the star, smashing a career-best 62 off just 32 balls, with four sixes and five fours.
Australian-born Johnston then returned bowling figures of three for 34 to deservedly take the man-of-the-match award, but was ably supported by opener Paul Stirling, who top-scored with a 43-ball 76.
Stirling and Johnston put on 64 in just over five overs for the third wicket.
Earlier, captain William Porterfield with 27 and Kevin O'Brien with 20 had kept the scoreboard ticking over.
In reply Afghanistan managed just 157 and were bowled out in 18.5 overs.
Gulbodin Naib struck 43 runs off just 19 balls and Mohammad Shahzad hit eight boundries and one six in a rapid 38, but the Asians lost their last four wickets for just 28 runs.
Hamza Hotak was the pick of their bowlers claiming three for 39.
In the third-fourth placed play-off Nepal beat hosts United Arab Emirates by five wickets.