The anti-inflammatory effects of phytochemicals, bioactive components from plants having health benefits, have been heavily investigated in the last several decades. However, the gap between the high dosage demands (μM) of phytochemicals in vitro studies and the low bioavailability (nM) of most phytochemicals after consuming relevant foods/supplements in humans undermines the application of these phytochemicals in the prevention of chronic inflammation and its related chronic diseases in humans. One of the approaches to bridging this gap is to combine two or more phytochemicals/foods to synergistically prevent chronic inflammation. While increasing combinations of phytochemicals on anti-inflammation studies have been reported, there is no report dedicating why combining two or more phytochemicals synergistically attenuates chronic inflammation. In the present review, we summarized different types of combinations exerting synergistic anti-inflammatory effects such as the combination of phytochemicals from the same foods, and the combination of phytochemicals from different foods/plants. Particularly, we proposed five mechanisms including enhancing the bioavailability of phytochemicals, increasing antioxidant capacity, interacting with gut microbiome and targeting same and different signaling pathways, to understand how the combination of phytochemicals exerts synergistic anti-inflammatory effects in cells, animals, and humans. This review provides clues to boost more studies to combine several phytochemicals/foods to reduce chronic inflammation and prevent chronic diseases in humans.