Well this is my work,Advice?It is good for a tank game?At this moment model doesn’t have texture 
I think 73000 polygons is a little high for a game object. I’d suggest making a lower poly model, and baking the one model onto the other.
Thank you for reply,i know i will try to remake it
I would probably create a lower poly version and use this one for high LoD. Also, I would recommend that before you place standard textures on it, create some solid AO maps to boost performance and appearance.
Before remaking it from scratch, take sdfgeoff’s advice, use the high poly model to bake your normal maps and apply them onto a low poly model. This will teach you a valuable lesson that you will be using throughout your blender game creations 
echoing what Saika said , your tank model is good high poly to bake from, as a matter of fact you could add even more detail on this version to add something something to your bakes…
40k is really pushing it especially if you want to have a nice looking terrain and more than one tank, i would suggest replacing the belt with just a texture as right now it looks like it is using up a lot of verts.
Something around 10k might be a bit more acceptable to have a stable running game. when modelling stuff for the game engine you want to make sure your using normal maps and a couple other types as this will make it look like your model is really high poly when it isn’t.
Also if you have any modifiers (ie. subdivision surface) i would suggest turning them off as these will increase the verts by a lot, the trick in the game engine is to use each vertice sparingly, for example the handles on your tank could just be cubes on smooth instead of cylinders this would drastically reduce the vertices and when textured shouldn’t really be noticeable.
Hope this helps