solved

There is block class

the block ID has to be below 256 to use it as a top or filler block.  This may change in the next version I think without block IDs but for now that's your issue. 

There is block class

Learn java.

You construct your Biome (

new

is the keyword to construct a new instance) before you construct the Block. But then in your Biome constructor you refer to the Block instance (which doesn't exist yet, it's null. That causes a NPE).

 

look:

 

BlockClass redstone:

 

public class BlockRedStone extends Block{
    public BlockRedStone(int blockID)
    {
    	super(blockID, Material.rock);
    	this.setCreativeTab(mod_SecretMod.tabSecretMod);
    	setHardness(4.0f);
    	setResistance(4.0f);
    	setStepSound(soundStoneFootstep);
    }

    @Override
    public void registerIcons(IconRegister iconRegister)
    {
            blockIcon = iconRegister.registerIcon("secretmod:RedStone");
    }

}

 

blockclass red grass:

 

public class BlockRedGrass extends Block{
protected Icon[] textures = new Icon[3];
    public BlockRedGrass(int blockID)
    {
    	super(blockID, Material.ground);
    	this.setCreativeTab(mod_SecretMod.tabSecretMod);
    	setHardness(4.0f);
    	setResistance(6.0f);
    	setStepSound(soundStoneFootstep);
    }
    
    public boolean isOpaqueCube()
    {
    	return false;
    }
    public boolean renderAsNormalBlock()
    {
    	return false;   	
    }
    public int getRenderBlockPass()
    {
    	return 1;
    }
    @Override
    public void registerIcons(IconRegister iconRegister)
    {
    	textures[0] = iconRegister.registerIcon("secretmod:grass_side");
    	textures[1] = iconRegister.registerIcon("secretmod:grass_top");
    	textures[2] = iconRegister.registerIcon("secretmod:dirt");
           
    }
    
    @Override
    public Icon getIcon(int side, int meta)
    {
    	if(side==0){
    		return textures[2];
    	} else if (side==1){
    		return textures[1];
    	} else if (side==2){
    		return textures[0];
    	} else if (side==3){
    		return textures[0];
    	} else if (side==4){
    		return textures[0];
    	} else if (side==5){
    		return textures[0];
    	} else {
    		return textures[0];
    	}
    }
}

Argh.

myBiome = new MyBiomeClass();
myBlock = new MyBlock();

That is what you have. Inside the MyBiomeClass constructor you have a reference to the myBlock field, which is still null at that point. Java executes your code from top to bottom.

 

I fix it, but when i create new world the biome is all iron ore

I fix it, but when i create new world the biome is all iron ore

the block ID has to be below 256 to use it as a top or filler block.  This may change in the next version I think without block IDs but for now that's your issue.

 

how to solve this? because I want to make the biome with a custom block