Almost a train a week on the South Coast line was cancelled in 2011-12, claimed NSW Shadow Transport Minister Penny Sharpe.
The opposition minister said there were 46 South Coast trains cancelled during that time, the worst of all intercity lines.
On the Sydney lines, the Eastern Suburbs was the worst with 97 cancellations, followed by the Illawarra line with 47.
MORE: Gong to Sydney train time to be cut
Overall, there were 425 cancellations for the period in question, Ms Sharpe said.
"These are the figures on CityRail train cancellations that the O'Farrell government hoped would stay secret," Ms Sharpe said.
"Barry O'Farrell promised to improve train reliability, yet the figures show that reliability is deteriorating."
She said the cancellations were mainly caused by mechanical issues, weather conditions and passenger disturbances.
"Barry O'Farrell has delivered the worst on-time running performance in four years and too many trains that simply never arrive," Ms Sharpe said.
NSW Transport Minister Gladys Berejiklian ridiculed Ms Sharpe's claims, stating the number of cancellations had dropped compared to what they were under Labor.
"The number of peak services cancelled has dropped significantly from the 580 cancellations under the former Labor Government a few years ago, so it is remarkable the Opposition have the hide to speak up on this issue," Ms Berejiklian said. Cancelled services last year made up less than half of 1 per cent of all peak services, she said.
"This government is working hard to improve the reliability of services, as well as customer service standards, through our Fixing the Trains initiative, which to date has also included the introduction of an extra 3000 train services each year," Ms Berejiklian said.