Can I only re-render a few object in the scene and keep others as they already rendered in the previous step

As the title. I just want to make a optional rendering in one frame. That mean I want to keep the color of some object in the previous rendering step, and omit the backgound change or anything I don’t want in current renderering step for some object.

Have you already tried to render your additional pass with a separate scene? This approach is used several times in the official examples (like in webgl_sprites). Some demos use a separate camera some reuse the one from the first call of WebGLRenderer.render(). So the pattern is:

renderer.clear();
renderer.render( scene1, camera );
renderer.clearDepth(); // optional
renderer.render( scene.2, camera );

This setup requires to set WebGLRenderer.autoClear to false. Otherwise you would lose the result of the first rendering.