If the American call option is exercised in advance, then the best time is to be able to exercise it in advance on the expiration date or any day before the expiration date or during the agreed period before the expiration date. The key feature of American options is that they can be exercised in advance on the expiration date or any day before the expiration date or the agreed period before the expiration date. For the pricing model of American options, the mainstream method is Barone-Adesi-Whaley quadratic approximation (hereinafter referred to as BAW model). The core idea of the model is to disassemble American options into European options and early exercise premium, and treat the early exercise premium itself as an option, which can be solved by partial differential equations.