A therapeutic agent comprising an isolated recombinant oncolytic adenovirus and an NK cell, an application, a kit, and a method for treatment of a tumor and/or cancer. The therapeutic agent comprises : a first pharmaceutical composition, the first pharmaceutical composition comprising a recombinant oncolytic adenovirus in a first pharmaceutically-acceptable carrier; and a second pharmaceutical composition, the second pharmaceutical composition comprising an NK cell in a second pharmaceutically-acceptable carrier. The recombinant oncolytic adenovirus is a replication-selective oncolytic adenovirus, and a coding sequence of exogenous shRNA capable of inhibiting PDL1 expression in tumor cells is integrated in a genome of the recombinant oncolytic adenovirus. The oncolytic killing effect of the recombinant oncolytic adenovirus and the anti-tumor immunostimulatory effect of a T lymphocyte produce a synergistic effect. Using the recombinant oncolytic adenovirus and the NK cell in combination can produce a further synergistic tumor-killing effect.