The visa validity is the length of time within which you are permitted to present your visa to a U.S. immigration inspector and request permission to enter at a United States port-of-entry. The visa does not guarantee entry to the U.S. The expiration date for the visa should not be confused with the authorized length of your stay in the U.S., given to you by the U.S. immigration inspector at port-of-entry, on the Arrival-Departure Record, Form I-94, or I-94W for the Visa Waiver Program. The visa expiration date has nothing to do with the authorized length of your stay in the U.S. for any given visit.
Travellers can enter the U.S. up to the day before their visa expires. Please make sure your current passport will be valid for 6 months from your date of entry into the U.S.
http://chinese.usembassy-china.org.cn/niv_faq1.html
The visa validity is the length of time within which you are permitted to present your visa to a U.S. immigration inspector and request permission to enter at a United States port-of-entry. The visa does not guarantee entry to the U.S. The expiration date for the visa should not be confused with the authorized length of your stay in the U.S., given to you by the U.S. immigration inspector at port-of-entry, on the Arrival-Departure Record, Form I-94, or I-94W for the Visa Waiver Program. The visa expiration date has nothing to do with the authorized length of your stay in the U.S. for any given visit.
签证的有效期是指在这个时间段内,您被允许在美国入境港口向美国移民视察员出示您的签证,并请求进入美国。持有签证无法保证您一定被准许进入美国。签证的到期日期不应与在美停留期限相混淆,该停留期限是由美国入境港口移民视察员在您进出境记录表(I-94表)上或发给免签国家公民的I-94W 表上所规定的。签证的到期日期与每次入境时获准在美停留的期限没有任何关联。
What does the validity of a visa mean?
Travellers can enter the U.S. up to the day before their visa expires. Please make sure your current passport will be valid for 6 months from your date of entry into the U.S.
"签证有效期" 是什么意思?
签证到期日之前, 旅行者皆可持该签证赴美。 同时,请确保您的护照距您预计抵美日期要有至少6个月的有效期。