In　this　paper,　we　study　the　channel　assignment　problem　in　cellular-VANET　heterogeneous　wireless　networks.　The　D2D　communication　technology　can　be　applied　to　VANET.　Vehicular　device-to-device　(D2D)　network　as　an　underlying　network　to　the　cellular　network　can　share　the　uplink　channel　resources　of　the　cellular　network.　Interference　as　a　critical　element　has　an　impact　on　the　utilization　in　channel　assignment.　To　minimize　the　interference　when　allocating　channels,　we　present　a　novel　channel　assignment　algorithm　based　on　reuse　distance.　Essentially　we　have　limited　spectrum　resources　that　can　be　shared　by　vehicular　transmitters　and　cellular　users　in　an　area,　to　assign　the　minimal　number　of　channels　to　vehicles　in　a　prescribed　area　is　our　first　concern.　Since　the　interference　between　co-channel　devices　is　related　to　their　distance,　we　divide　the　area　to　small　hexagon　regions　then　use　Region-based　Channel　Assignment　Algorithm　to　assign　different　channel　sets　to　each　region.　In　this　case,　three　sets　of　resources　can　fulfill　the　channel　assignment　requirements　to　all　vehicles.　We　also　prove　the　theoretical　guarantee　as　approximation　factor　of　3　for　the　minimal　channel　assignment　problem.　To　improve　the　system　throughput　with　limited　channel　resources　in　the　HetNets,　we　propose　a　Local　Search　Throughput　Maximization　algorithm　to　find　the　vehicular　transmitters　and　cellular　users　combinations.　We　prove　the　optimal　approximation　factor　is　(1-c)　and　the　complexity　of　our　algorithm　in　each　small　region.　We　show　the　effectiveness　and　efficiency　of　proposed　algorithm　in　experiments.