Artificial Intelligence has been a very popular topic at present, machine learning is also one of the main algorithms in AI, which consisted of Supervised learning, Unsupervised learning and Reinforcement learning, and Supervised learning and Unsupervised learning have been relatively mature. Reinforcement learning technology has a long history, it wasn't until the late '80s and early' 90s that reinforcement learning became widely used in artificial intelligence, machine learning. Generally, Reinforcement learning is a process of trial and error, agent will choose to make an action according to the feedback from the environment, this step will repeat a lot of times until it find the best policy, mapping it to reality, it can help human to fulfill some missions which are nearly impossible before. However, there is still some potential problems in Reinforcement learning. This essay compares some basic algorithms related to RL to help reader to have a basic understanding of RL and propose some exsiting defects about it.