Novae undergo a supersoft X-ray phase of varying duration after the optical outburst .
Such transient post-nova supersoft X-ray sources ( SSSs ) are the majority of the observed SSSs in M31 .
In this paper , we use the post-nova evolutionary models of Wolf et al .
to compute the expected population of post-nova SSSs in M31 .
We predict that depending on the assumptions about the WD mass distribution in novae , at any instant there are about 250 – 600 post-nova SSSs in M31 with ( unabsorbed ) 0.2–1.0 keV luminosity L _ { x } \geq 10 ^ { 36 } erg/s .
Their combined unabsorbed luminosity is of the order of \sim 10 ^ { 39 } erg/s .
Their luminosity distribution shows significant steepening around \log ( L _ { x } ) \sim 37.7 – 38 and becomes zero at L _ { x } \approx 2 \times 10 ^ { 38 } erg/s , the maximum L _ { x } achieved in the post-nova evolutionary tracks .
Their effective temperature distribution has a roughly power law shape with differential slope of { \approx 4 \mbox { - - } 6 } up to the maximum temperature of T _ { eff } \approx 1.5 \times 10 ^ { 6 } K .

We compare our predictions with the results of the XMM-Newton monitoring of the central field of M31 between 2006 and 2009 .
The predicted number of post-nova SSSs exceed the observed number by a factor of { \approx 2 \mbox { - - } 5 } , depending on the assumed WD mass distribution in novae .
This is good agreement , considering the number and magnitude of uncertainties involved in calculations of the post-nova evolutionary models and their X-ray output .
Furthermore , only a moderate circumstellar absorption , with hydrogen column density of the order of \sim 10 ^ { 21 } ~ { } { cm } ^ { -2 } , will remove the discrepancy .