On the basis of the theory of option pricing,We study the connection between America call option and European call option;Under the assumption condition of Black-Scholes formula ,use the theory of martingales and stopping time,get the conclusion that: the price of America call option equals the price of European call option; Discuss some numeric computing methods of the put America option pricing, with the invarional inequaility for optimal stopping, prove the boundary property of America put option price and introduce some numeric computing methods of the put America option price.