The invention discloses a mixed rolling method based on a CSP process for strip steel with different width specifications. The mixed rolling method comprises the following steps: setting and correcting the width of a casting blank; determining the tapping temperatures of a casting starting blank and a roll-changing rolling starting blank; determining control parameters of a loop; adjusting rolling parameters; and determining a rolled steel plate to be a qualified product when the actual width of the rolled steel plate is greater than a width in an order form and not greater than 20mm, and disposing a rolled steel plate as an unqualified product when the actual width of the rolled steel plate is less than or greater than the width in the order form and greater than 20mm. According to the mixed rolling method disclosed by the invention, the setting accuracy of the width of the casting blank can be improved through correcting the initial value of the width of the casting blank; a calculated tapping temperature of a plate blank is optimized to solve the problem of insufficient width of the head part of the strip steel; meanwhile, the angle of the loop is adjusted to solve the problem of insufficient width of the tail part of the strip steel; and real-time adjustment is carried out on the width through adopting the measures of vertical roll side pressing, tension increasing and the like, so as to increase the production efficiency, save energy and reduce consumption, improve the hitting accuracy of the width of the strip steel and increase the timely completion rate of a contract.