The flat topping width pulses are obtained by the method of twitter pulse stack. According to the approximately equation of the pulse transmission equation,the transmission characteristic of the stack pulse in linear medium have been analyzed theoretically,and the time profile change rule of the tack pulse are given. It is show that the stack pulse envelope antithetical couplet pulse delay parameter is unstable. If the twitter is greater,the sub-pulse initial pulse width is shorter,and the transmission medium dispersion coefficient is bigger,then the stack pulse time modulation become more serious after the transmission.