Legal analysis: the letter of guarantee is a subsidiary contract attached to the main contract, and the relevant provisions of the Civil Code apply. As long as the content of the guarantee is not illegal, the guarantee has legal effect after both parties reach an agreement through consultation and the guarantor signs or seals it.

Legal basis: Article 143 of the Civil Law of People's Republic of China (PRC) A civil juristic act that meets the following conditions is valid:

(1) The actor has corresponding capacity for civil conduct;

(2) the meaning is true;

(three) does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.