In　this　paper,　a　generalized　combined　power　and　natural　gas　network　risk　assessment　model　is　proposed　for　quantifying　its　risk　level　considering　dangerous　factors　such　as　generation　outages,　transmission　line　contingencies,　natural　gas　pipeline　contingencies,　compressor　failures　and　gas　source　and　load　fluctuation.　This　evaluation　model　statistics　the　specific　electricity　and　gas　load　loss　in　reliance　on　a　state-based　non-sequential　Monte　Carlo　method,　it　aims　at　minimizing　the　Cost　of　Lost　Load　(COLL)　of　the　combined　system　based　on　the　security-constrained　steady-state　analysis.　Usually,　the　model　is　non-linear　and　non-convex,　to　overcome　the　problem＇s　non-convexity,　an　increment　based　mix　integral　linear　programing　(IMILP)　is　employed　to　effectively　and　accurately　solve　the　COLL　minimization　optimization　model.　Besides,　a　specific　customized　reliability　indexes　are　developed　to　comprehensively　assess　the　risk　from　cost,　gas　and　electricity　loss　three　dimensions.　At　last,　the　evaluation　model　is　verified　by　a　one　combined　6-node　electricity　network　and　14-node　gas　network　test　case.　The　results　show　that　the　proposed　model　can　quantitatively　assess　the　effect　of　those　uncertainties　on　the　combined　system　risk　level.　©　2018　IEEE.