The posts have been lost through compulsory and voluntary redundancies, recruitment freezes and deletion of vacant posts, according to an RCN report.
The report, Our NHS - today and tomorrow, states: 'Contrary to the argument often put forward by the government, lost posts are not natural wastage.
'If a post is deleted or a nursing vacancy isn't filled, that workload will have to be taken up by the nursing workforce in that trust.'
There had been 22,363 posts lost, the RCN said, with the fewest in the North West (1,059) and the highest in London (3,628).
It said a 'rip-tide of deficit-led cuts, rushed reforms and poor workforce planning' was 'hitting services, hurting patients, undermining staff morale and threatening the hard-won progress made over recent years'.
The report said cash taken from training and public health budgets to pay off deficits posed a 'long-term threat to patient care and public health'.
The document, which has been sent to all MPs, offers 'RCN solutions' such as creating a centrally provided 'buffer' fund to achieve financial balance for trusts.
The RCN has also published findings of an online survey it commissioned from pollsters YouGov.
Of the 2,400 members of the public questioned, 37 per cent said health should be the most important spending priority for the next government.
Nearly two-thirds, 59 per cent, said NHS spending should be increased and 5 per cent said it should be reduced.
But those polled were split down the middle over whether the NHS had improved during the past 10 years. While 36 per cent believed there had been an improvement, the same proportion disagreed.
Respondents were also split over moves to create competition and a market in the NHS, with 47 saying it would break up the health service. Meanwhile 46 per cent said the government should introduce a dedicated NHS tax.