The factors affecting option pricing under regime switch market are studied, firstly the trinomial model for option pricing under regime switch market is analyzed and studied, its rationality is proved, from this we derive that the factors affecting option pricing under regime switch market mainly include generator matrix and the difference value of volatility rate under different modes, then numerical example and Matlab programs are used to verify the impact of volatility rate on option pricing with regime switch while numerical example is used to illustrate the influence of generator matrix on option pricing as generator matrix is symmetric matrix.