So i made a custom model (the size is like 5.3). But the textures is look so blurry

This is the actual file :

This is something OptiFine does. When you have a non-power-of-2 sized texture in vanilla it disables mipmapping, whilst OptiFine and Forge both scale the texture up to a power-of-2 to retain the mipmapping on it. Because of this though the resulting texture will be blured as it gets scaled back again in game.

There's a bit more about it here: sp614x/optifine#1982