There aren't any forms of barley that are gluten-free, including pearl barley. Gluten naturally occurs in barley, wheat, and rye, and it cannot be removed.
Pearl Barley and Gluten
Pearl barley is barley that has the hull and bran removed because it is polished as it is processed. However, just because these two components of the grain are removed doesn't mean pearl barley doesn't contain gluten like whole barley does. In fact, pearl barley contains the gluten proteins that pose a problem for people with celiac disease or non-celiac gluten-intolerance. If you are avoiding gluten, you should avoid this ingredient and any foods that contain it.
Gluten-Free Substitutes for Pearl Barley
Pearl barley is often added to soups and stews, and it is used in grain side dishes and cereals, as well. Because barley is a grain, there is no gluten-free version unlike other gluten-containing ingredients like couscous or pasta. However, you can use other ingredients in place of barley in dishes. Typically, pearl barley takes as long as 40 minutes to cook, so many of the substitutes are much quicker cooking. For best results using any of the substitutes below, use an equal amount to the barley required in the recipe and adjust cooking times according to package directions, which may mean you need to add it sooner or later to recipes than the pearl barley.
Rice is always a good choice because it is naturally gluten-free as long as it is processed in a plant that doesn't also process gluten-containing ingredients. Brown rice may yield the closest flavor and texture to pearl barley.
Although its name sounds a lot like a gluten-containing ingredient wheat, buckwheat is actually a seed closely related to sorrel and not related to wheat at all, so it is safe for people in a gluten-free diet. Use buckwheat groats (also called whole buckwheat) as a direct replacement for pearl barley and adjust cooking time according to package directions.
Quinoa is made from the edible seeds of a plant in the amaranth family. It has a nutty flavor and shape similar to pearl barley (although the grains are a little smaller), making it a good substitute. Use an equal amount and adjust cooking times according to package directions.
Millet is small seeds from grasses, and it is gluten-free. The seeds are much smaller that pearl barley, so the texture will be different in the finished dish, but flavor-wise it is an acceptable substitute. Use a direct measurement substitution and adjust cooking times according to package directions.
If you're on a gluten-free diet, pearl barley (or any other type of barley) isn't a good choice because of its naturally occurring gluten content. However, with a little creativity it's easy to find substitutes that will still have the taste and texture you desire.