Sweden forward Fridolina Rolfo put the Germans ahead against the run of the play in the 58th minute, firing in from close range as Barca, beaten finalists last year, failed to clear the danger.
Barca had 16 attempts on goal but only once managed to test Wolfsburg keeper Friederike Abt, who saved a header from Nigerian forward Asisat Oshoala in the first half which appeared to deflect off the hand of Wolfsburg defender Kathrin Hendrich, but the Spanish side's appeals for a penalty were ignored.
Oshoala headed narrowly over the bar soon after Rolfo's goal while Spain internationals Mariona Caldentey and Jennifer Hermoso also missed the target.
'I've not felt the support of the club' - Koeman on Barca board
Wolfsburg saw the game out to book their place in the final on Aug. 30 against either holders Olympique Lyonnais or Paris St Germain, who meet on Wednesday.
Xavi in talks with Barca over replacing Koeman - reports
Women's Champions League
Barcelona dismantle Chelsea in Champions League final