When you read something in English, do you translate it into Mandarin in your head so you can understand it? If you do, try rushing through the English reading. You are more likely to skip the mental translation step. However, words that you don't know from the text might make you feel like your understanding is a bit blurry. If you keep seeing the same word and you can't figure it out in the context of the reading, then look it up. Otherwise, if you don't know one word and it is not affecting your understanding of the text as a whole, don't worry about looking it up.
Try these suggestions. They will probably make you read a little bit faster.