The invention relates to a source applicator for anal canal tumor radiotherapy, the source applicator comprises a cylindrical source applicator body of which the diameter is 3cm, wherein the front end of the source applicator body is a spherical arc, the front segment of the source applicator body is a right cylinder segment of which the length is 8.5cm, the right cylinder segment comprises the spherical arc at the front end, the rear segment of the source applicator body is bent in a manner of a 150-degree arc, the arc length of an introvert of an arc-shaped bent segment is 5cm, the source applicator body is internally and axially provided with three source applying tubes which are eccentrically arranged in a semicircle of the introvert side of the cross section of the source applicator body and distributed in a manner of a circular curve, and the distance between the center of each source applying tube and the outer wall of the introvert side of the source applicator body is 5.5cm; an arc between the circle center of the first source applying tube and the circle center of the second source applying tube is equal to an arc between the circle center of the second source applying tube and the circle center of the third source applying tube, and a central angle corresponding to the arc is 60 degrees. The source applicator has a good radiotherapy effect on nidus that part carcinoma of the anal canal spreads outside the anus edge, reduces the possibility of tumor recurrence and facilitates radical cure of the tumor.