The best chance for Reading, who face Arsenal in the Cup at Wembley next Saturday, fell to Jamie Mackie in the first half but his header went over.
Blackburn barely threatened throughout a scrappy match but home keeper Adam Federici did have to tip over a dangerous cross from Ben Marshall.
Reading manager Steve Clarke had one eye on the trip to Wembley, resting usual left back Jordan Obita.
Obita has nine yellow cards this season and, should he have collected a 10th against Blackburn, he would have missed the semi-final due to suspension.
Blackburn could also have made the last-four of the Cup but lost a quarter-final replay 1-0 to Liverpool at Ewood Park on Wednesday night.
Reading have been in ragged form, with just two wins in their past 11 league games, but began brightly.
An early corner from Garath McCleary on the right found Alex Pearce in the Blackburn area but the centre back’s header flew high and wide.
Mackie crossed low and hard, also from the right, but Hal Robson-Kanu’s first-time effort was gathered easily by Blackburn keeper Simon Eastwood.
Blackburn had won four of their previous six league games but, with the play-offs well out of their reach, they appeared lacking in motivation.
Even 17-goal Jordan Rhodes struggled to make any headway up front as the home defence enjoyed a comfortable first half.
Reading persevered going forward but were off target again, Nathaniel Chalobah twice wasting good openings with poor shots from distance.
Another chance fell to Mackie. McCleary chipped over a cross from the left but Mackie’s header looped narrowly over the bar.
Reading ended the half with a flurry. Captain Jem Karacan, making his first start in 19 months after knee problems, had a shot blocked.
Robson-Kanu then drove over and a strong Tommy Spurr tackle denied Pavel Pogrebnyak from a Mackie cross.
Blackburn improved after the break and at last managed to create a threat moving forward.
Marshall steadied himself just outside the home area but his goalbound effort was cleared to safety by Chris Gunter.
Blackburn went even closer when Marshall chipped over a cross from the left. It seemed to be dipping under the bar but Federici managed to tip it over.
Reading swiftly resumed control and twice went close. A Mackie cross evaded everyone in the Blackburn area – as did a fiercely driven McCleary corner from the left.
Pogrebnyak raced clear of the Blackburn defence near the end but, at the vital moment, slipped over and lost all chance of a winner as Reading gained their third successive draw.