只有持有英国访问签证的人，去爱尔兰短期访问才不要签证，其他类型的英国签证不行，要另外签证。我拷贝给你看一个文件，是爱尔兰大使馆官方的文件：
The Short-stay Visa Waiver Programme

Information Note

The Short-stay Visa Waiver Programme was announced by the Government as part of its Jobs
Initiative with a view to promoting tourism from emerging markets. It is due to commence on
1 July 2011. The programme will run as a pilot up to end October 2012 but may be amended
or expanded at any point depending on experience of the pilot.
The main points of the programme are:

Persons granted leave to enter the UK (i.e. granted a “UK visa”) as a general visitor,
child visitor, business visitor or sporting visitor will be able to travel to Ireland within
the period of validity of their leave to remain in the UK without the requirement to
obtain an Irish visa.

The period of validity of leave to remain in the UK for the above categories is 180 days
but the maximum stay in Ireland will be 90 days or to the end of the period of validity
of the UK leave to remain, whichever is the shorter. It should be stressed that the need
for a visa to visit Ireland is not eliminated by this programme. Visitors from visarequired
countries will still require an Irish visa (for direct travel to Ireland) or a UK
visa (for travel to Ireland via the UK). What is eliminated by this programme is the
need to have both an Irish and UK visa when visiting Ireland via the UK.
The person travelling will be required to land in and have gained lawful entry to the
UK, on foot of the current leave to enter (visa), prior to travel to Ireland. Lawful entry
will be attested by the appropriate entry stamp of the UK Border Agency. Therefore,
transit passengers through the UK to Ireland, who do not pass through immigration in
the UK, will still require an Irish visa. There is no minimum length of stay in the UK
required before travel to Ireland.