我持中国护照，有加拿大绿卡，现在在美国工作H1-B. 入境签证是在加拿大的美国使馆拿的，每次拿美国签证都有2周的调查期。I-94是3年， 我的入境签只有2次，10月中旬就作废了。如果我理解正确的话，只要在30天之内，我可以自由往返于加拿大和美国之间无论是走陆路还是飞机。但好像不可以从别国回到加拿大再到美国。我很想明年初有假了回国看看父母（本来想来美国之前回去的，假没请下来）。 哎，出国10年了，没想到最后被卡到了美国，还是美国牛啊。在这里恳请皮匠老师出个主意建议啥的，谢谢了。
下面是美国大使馆发过来的信，第六条没看懂。
READMISSION TO THE UNITED STATES
Automatic revalidation of non-immigrant visas in certain cases
Persons in non-immigrant status in the United States, even if their original visas have expired, may reapply directly for admission to the United States with the Immigration and Naturalization Service after a stay in either Canada or Mexico of less than thirty (30) days. They must however meet the following conditions:
1) The applicant has been previously admitted to the United States as a non-immigrant and is in possession of an expired or unexpired visa issued pursuant to any part of Section 101(a)(15) of the Immigrant and Nationality Act (Visa categories – A, B, C, D, E, F, G, H, I, J, L, M, N, O , P, Q AND R) or has had his status changed by the United States Immigration Service to any one of these categories while in the United States.
2) The applicant is in possession of a Form I-94 (Arrival-Departure Card) endorsed by the Immigration and Naturalization Service to show an unexpired period of initial admission or extension of stay in the United States. ( The applicant may be readmitted by the Immigration Service only for the remaining period of validity shown on Form I-94)
3) He has remained solely in contiguous territory, that is in Canada or Mexico, and has not travelled to other countries.
4) The applicant intends to resume the non-immigrant status for which he was previously admitted or to which his status was previously changed by the Immigration Service.
5) The applicant must be in possession of a passport valid, in general, for at least six months beyond the duration of his stay in the U.S.
6) The original admission or readmission of the applicant cannot have been made on the basis of a prior authorization or waiver from the Immigration and Naturalization Service because the applicant was ineligible for admission under Section (212)(a) of the Immigration and Nationality Act.
No fee will be charged in applicable cases for readmission under these circumstances.