Ben Roethlisberger has the most passing yards by a Steelers quarterback in a game, with 522 yards against the Colts on October 26, 2014.

which steelers qb has the most passing yards in a game
Interpreted as:
Which steelers qb has the most passing yards in a regular-season game?
10/26/2014Roethlisberger12/10/2017Roethlisberger12/20/2009Roethlisberger11/10/2002Maddox11/25/2018Roethlisberger11/29/2015Roethlisberger9/16/2018Roethlisberger11/30/2014Roethlisberger11/5/2006Roethlisberger10/18/2009Roethlisberger12/13/1958Layne11/13/2016Roethlisberger9/22/2013Roethlisberger11/3/2013Roethlisberger11/22/2009Roethlisberger11/14/2010Roethlisberger12/4/2005Roethlisberger9/23/2012Roethlisberger9/29/2013Roethlisberger12/23/2018Roethlisberger10/9/2016Roethlisberger12/20/2015Roethlisberger522506503473462456452435433417409408406400398387386384383380380380
NAMEDATETMOPPYDSCMPATTPCTAVGTDTD%INTINT%SCKSCKYRATE
Ben RoethlisbergerBen Roethlisberger10/26/2014
PITPIT
vs
INDIND
522404981.610.7612.200.000150.6
Ben RoethlisbergerBen Roethlisberger12/10/2017
PITPIT
vs
BALBAL
506446666.77.723.000.032099.7
Ben RoethlisbergerBen Roethlisberger12/20/2009
PITPIT
vs
GBGB
503294663.010.936.500.0531121.9
Tommy MaddoxTommy Maddox11/10/2002
PITPIT
vs
ATLATL
473284168.311.549.812.4210129.4
Ben RoethlisbergerBen Roethlisberger11/25/2018
PITPIT
@
DENDEN
462415673.28.311.823.621288.5
Ben RoethlisbergerBen Roethlisberger11/29/2015
PITPIT
@
SEASEA
456365565.58.311.823.621082.1
Ben RoethlisbergerBen Roethlisberger9/16/2018
PITPIT
vs
KCKC
452396065.07.535.000.0110104.3
Ben RoethlisbergerBen Roethlisberger11/30/2014
PITPIT
vs
NONO
435325855.27.523.423.41076.4
Ben RoethlisbergerBen Roethlisberger11/5/2006
PITPIT
vs
DENDEN
433385470.48.011.935.643077.2
Ben RoethlisbergerBen Roethlisberger10/18/2009
PITPIT
vs
CLECLE
417233565.711.925.712.9314113.6
Bobby LayneBobby Layne12/13/1958
PITPIT
vs
CHCCHC
409234946.98.324.136.164.1
Ben RoethlisbergerBen Roethlisberger11/13/2016
PITPIT
vs
DALDAL
408374680.48.936.500.018125.4
Ben RoethlisbergerBen Roethlisberger9/22/2013
PITPIT
vs
CHICHI
406264163.49.924.924.932792.1
Ben RoethlisbergerBen Roethlisberger11/3/2013
PITPIT
@
NENE
400284858.38.348.324.252995.8
Ben RoethlisbergerBen Roethlisberger11/22/2009
PITPIT
@
KCKC
398324276.29.537.124.8213109.0
Ben RoethlisbergerBen Roethlisberger11/14/2010
PITPIT
vs
NENE
387304961.27.936.112.053897.9
Ben RoethlisbergerBen Roethlisberger12/4/2005
PITPIT
vs
CINCIN
386294170.79.437.337.32794.2
Ben RoethlisbergerBen Roethlisberger9/23/2012
PITPIT
@
OAKOAK
384364973.57.848.200.015123.2
Ben RoethlisbergerBen Roethlisberger9/29/2013
PITPIT
@
MINMIN
383365170.67.512.012.052690.6
Ben RoethlisbergerBen Roethlisberger12/23/2018
PITPIT
@
NONO
380335066.07.636.000.0316108.8
Ben RoethlisbergerBen Roethlisberger10/9/2016
PITPIT
vs
NYJNYJ
380344772.38.148.500.015124.4
Ben RoethlisbergerBen Roethlisberger12/20/2015
PITPIT
vs
DENDEN
380405572.76.935.523.632694.5
Ben RoethlisbergerBen Roethlisberger11/15/2015
PITPIT
vs
CLECLE
379223366.711.539.113.013123.2
Neil O'DonnellNeil O'Donnell11/19/1995
PITPIT
@
CINCIN
377243177.412.239.700.0112149.5
Ed BrownEd Brown10/27/1963
PITPIT
vs
DALDAL
377153148.412.2412.939.793.1
Results may be incomplete. StatMuse has complete game-level data for passing yards going back to the 1950 season.