Adjusted cosine similarity is a kind of more advanced calculation method. As for cosine similarity the calculation, the fact that users have different rating standards (or some users have high scores and some users have low scorer) is not considered. Adjusted cosine similarity makes up for the above defect. To be specifific, it fifirst adjusts the score vector for grading deviation vector through the calculation of the average score of every user, and then solves the cosine similarity, with the formula listed below: