A Φ1200mm colorful schlieren system was designed by adopting an illumination system without any protecting windows. The theoretical optical model of the Φ1200mm colorful schlieren system was built up and the imaging uniformity of the system was studied under the complex working conditions as the gravity, temperature variation, and ambient pressure. The three typical combinations of the slit width and the cutting quantity of the knife had been considered here, which are 2mm slit width with 1/4 cutting quantity , 2mm slit width with 1/2 cutting quantity, and 0.5mm slit width with 3/4 cutting quantity. With above three combinations, the imaging uniformity of the system was analyzed under the ideal working condition and under the condition by the consideration of integral error respectively. The results show that with the consideration of integral error, the uniformity of the schlieren image is decreased compared with that of the ideal working condition. With the consideration of integral error, when the system is under relatively low sensitivity, the range of the non-uniformity is from －2.44% to 2.45%; under relatively normal sensitivity, the range of the non-uniformity is from －3.43% to 3.45%; under relatively high sensitivity, the range of the non-uniformity is from －5.76% to 5.81%.