北师大版高中英语选修7 Unit20:

二者都有“拯救、挽救、援救、营救”的意思：

rescue (to help someone or something out of a dangerous, harmful or unpleasant situation) 含义较广，常和from连用。一般多用人，该词偶尔用于某物时，指采取措施防止被毁灭或被损坏。

rescue somebody from danger 营救某人脱险

They rescued the wounded soliders from captivity. 他们营救伤员，使他们免于被俘。

He dives from the bridge to rescue the drowning child. 他从桥上跳入水中去抢救那溺水儿童。

They have taken steps to rescue the building from fire.他们已采取措施抢救房屋，使其不致烧毁。

save (to stop someone or something from being killed, injured or destroyed) 泛指帮助、拯救，含有使之得以保全、存活或继续使用的意味。

He had to borrow money to save his business.他不得不借钱挽救他的生意。

He saved her life ever. 他曾经救过她的命。

两者若不细分，两者常可换用。