中國出兵朝鮮和蘇聯空軍參加朝鮮戰爭作戰，構成了中蘇共同援助朝鮮及蘇中朝三角同盟形成的基礎。近年來披露的中國和俄國檔案，為揭開這一歷史謎團提供了大量文獻證據。在朝鮮戰爭初期，美國參戰，迫使中蘇兩國領導人都想到了中國出兵的問題。為此，史達林承諾蘇聯出動空軍掩護中國地面部隊，卻沒有說明出動的時間和方式；仁川登陸前，毛澤東就想派兵參戰以便儘快結束戰爭，但史達林並不急於使用中國軍隊，因為這涉及到蘇聯出動空軍及其在朝鮮的地位和影響；在三八線被突破的危急時刻，毛澤東希望立即出兵援朝，而史達林擔心蘇聯與美國發生直接的軍事衝突，也懷疑毛澤東出兵的誠意和效果，故拒絕出動空軍；中國志願軍毅然出動並獨自與美韓軍隊作戰後，蘇聯空軍也隨即投入了戰鬥，不僅保護中國領空，而且越過鴨綠江為志願軍後方提供掩護；關於蘇聯空軍參戰，史達林堅持不變的原則是：無論是否越過鴨綠江，蘇聯空軍只在後方活動而絕不進入前線配合中國地面部隊作戰。從中國出兵和蘇聯空軍參戰的過程可以看出，中、蘇、朝之間的關係非常微妙，這一同盟的基礎也十分脆弱。

China's entry into the Korean War and the involvement of the Soviet air forces in the war constituted the basis of China's and the Soviet Union's joint assistance to North Korea as well as the formation of the Sino-Soviet-North Korean triangular alliance. Recently declassified archives in China and Russia have provided a great amount of documentary evidence for historians to uncover the mystery surrounding the historical event. In the beginning period of the Korean War, the American intervention compelled the Chinese and Soviet leaders to contemplate the possibility of sending Chinese forces to intervene the war. Stalin had promised to send Soviet air forces to cover Chinese ground forces, without, however, specifying the timing and method of dispatching Soviet forces. Before the American forces' landing on Incheon, Mao Zedong had wanted to send the Chinese forces with an aim of ending the war as soon as possible. However, Stalin did not want to use the Chinese troops in hurry, partly because it involved the Soviet commitment to dispatch air forces and the Soviet position and influence in North Korea. At the crucial moment when the American forces crossed the 38th parallel, Mao Zedong wished to send out Chinese troops immediately. However, Stalin worried about the possibility of direct military confrontation between the Soviet Union and the United States. Moreover, the Soviet leader was suspicious of Mao's sincerity in sending Chinese troops as well as the effectiveness of doing so. Therefore, Stalin refused to dispatch the Soviet air forces. However, after Chinese troops entered into the Korean peninsula and confronted directly the American and South Korean troops, Moscow dispatched air forces to join the battle, which not only protected Chinese territorial air space, but also provided cover for the rear of the Chinese troops. One of Stalin's unyielding principles, however, was that regardless of whether who would cross the Yalu River or not, the Soviet air forces would only act in the rear area and not involve themselves in frontier battles. It can be shown from the process of China's sending out troops and the Soviet air forces' joining the war that the triangular relations among China, the Soviet Union and North Korea were extremely delicate, and that the basis of such a triangular alliance was quite weak.