中国西部地区包括12个省市及自治区，即西南五省区市（重庆、四川、云南、贵州、西藏）、西北五省区（陕西、甘肃、青海、新疆、宁夏）和内蒙古、广西。总面积约686万平方公里，约占全国总面积的 72%。

再来看Wikipedia对“Western China”的定义如下：Western China (simplified Chinese: 中国西部; traditional Chinese: 中國西部; pinyin: Zhōngguó Xībù; lit. 'China-west', or rarely simplified Chinese: 华西; traditional Chinese: 華西; pinyin: Huáxī; lit. 'Huaxia-west') is the west of China. In the definition of the Chinese government, Western China covers one municipality: Chongqing; six provinces: Sichuan, Guizhou, Yunnan, Shaanxi, Gansu, and Qinghai; and three autonomous regions: Tibet, Ningxia, and Xinjiang.

其中有句话：Western China is the west of China，可见“中国西部”既可以表达为“Western China”也可以表达为“the west of China”。

e.g.

It should also be noted that the gap of economic development between Eastern China and Western China has been expanding.

还应该注意的是，中国东部与中国西部经济发展的差距一直在拉大。

In addition, to take advantage of the rapid development of the western China market, the Group intends to establish an office in Chengdu to complement its strategically located distribution centres in Shenzhen, Wuxi and Guangzhou.

另外，在中国西部大开发的有 利环境下，集团将于成都设立办事处，于当地占一席位，以配合集团深圳、无锡和广州策略营销中心的运作。

需要注意的是，“中国西部”译为“the west of China”时，一般会加定冠词“the”。可参考《柯林斯英汉双解大词典》对其的释义：The west of a place, country, or region is the part of it which is in the west.

e.g. Many of the buildings in the west of the city are on fire.

 该城西部的许多建筑都着火了。