The Pope's letter will be released today.In his message, the Pope is stretching out a hand of friendship to the Catholics, who are divided in their loyalties to Beijing and to Rome.
There are some 10-15m Catholics in China - a tiny minority among a total population of 1.3bn people.
Beijing broke diplomatic ties with the Vatican more than 50 years ago after the Communist takeover.
The letter, which has already been sent to the authorities in China, is one of the boldest diplomatic and pastoral initiatives of Benedict's reign so far.
In his 28-page document, the Pope pointedly refrains from referring specifically either to the underground church, which is still in communion with Rome, or to the Patriotic Catholic Church, whose bishops have always been appointed from Beijing.
The Pope's aim is to normalise relations with Beijing.
The Vatican regards China as a country with huge missionary potential, and has been holding informal talks for several years with Chinese officials with a view to restoring diplomatic relations.
The Pope's letter discusses religious freedom in China - a touchy subject for the Beijing authorities.
Bishops of the officially-tolerated Patriotic Catholic Church have been called to Beijing to discuss how to react to the Pope's message.
Apart from the dispute over the appointment of Chinese bishops, the main stumbling block to the restoration of relations has been Rome's recognition of Taiwan.
The Beijing authorities insist that Rome must first break with Taiwan before a Papal nuncio can take up residence again in Beijing.