The invention relates to a propellant pipe cross conveying system. The propellant pipe cross conveying system comprises an oxidizing agent one-way valve (1), a first oxidizing agent isolating valve (2), an oxidizing agent separating valve (3), a second oxidizing agent separating valve (4), an oxidizing agent cross conveying pipe (5), an incendiary agent one-way valve (6), a first incendiary agent isolating valve (7), an incendiary agent separating valve (8), a second incendiary agent isolating valve (9), an incendiary agent cross conveying pipe (10), an incendiary agent starting isolating valve (11), an oxidizing agent starting isolating valve (12), a boosting incendiary agent conveying pipe (13), a boosting oxidizing agent conveying pipe (14), a core first-stage oxidizing agent conveying pipe (15) and a core first-stage incendiary agent conveying pipe (16). According to the propellant pipe cross conveying system, the carrying capacity of a liquid carrier rocket can be improved, and the efficiency of a three-stage rocket can be achieved by the propellant pipe cross conveying system. During the boosting flying period, when one engine breaks down, propellants can be continuously conveyed to other engines through the cross conveying pipes to be used, and the power system redundancy is accordingly achieved.