The accounts, filed with Companies House last week, show the charity had an income of £100.2m in the calendar year, down from £102.8m in the previous 12 months.
Total income from donations and legacies was £92.4m, down from £98m in 2016.
Income from corporate partnerships fell by almost £3m year on year to £13.8m, and income from special events was down by £3.1m to £1.5m.
But direct marketing income rose by £2.8m to £44.3m and income from major supporters, charitable trusts and foundations was up by £5.2m to £21.6m in 2017.
Total spending was £102.9m, down from £103.4m in the previous year.
The accounts say 2017 was a year of "profound political, social and economic upheaval and uncertainty".
They say that it was the third successive year the charity had raised more than £100m, an achievement that was made more remarkable "because of the changes and challenges in the fundraising environment in the UK".
The accounts say the charity worked with the Boston Consulting Group to conduct an analysis of external factors and trends in the social impact and voluntary giving sectors.
"Unicef UK is operating in an increasingly challenging and complex environment, not least due to wider economic and political uncertainty that the UK is experiencing," according to the report.
"The UK is also seeing evidence of a widening in social divide and views have become more polarised. An obvious area of concern in this context is the maintaining of UK overseas aid levels, which provide a significant proportion of funds to Unicef."
The fundraising market is expected to grow only marginally over the coming year, the accounts say.
"This sector is also highly competitive and has been affected by negative media publicity, which has contributed to a fall in trust in charities and NGOs," the accounts say.
The charity’s highest earner is identified in the accounts as executive director Mike Penrose, who received gross pay of £115.492 plus pension contributions of £4,676 in the year.