A biotrickling filter for treating waste gas including a waste gas inlet, packing layers, a spray pipe, a spray liquid storage tank, and a waste gas outlet. The waste gas passes through a first packing layer after passing through the waste gas inlet and then passes through a second packing layer after changing the flow direction at the bottom of the first packing layer; the flow directions of the waste gas in the first packing layer and the second packing layer are opposite to form a cross-flow structure; the two different flow directions of the waste gas form a cross-flow unit, and two or more cross-flow units form the biotrickling filter.