To address the problem that the signal-to-noise ratio and stage linearity of the imaging circuit system under the horizontal uniform subdivision and summation timing do not meet the requirements of the camera specifications, based on the analysis of the characteristics and working principle of the ultra-large pixel TDICCD, this article proposes a design scheme for the horizontal non-uniform subdivision and summation timing. This scheme conducts timing optimization and software design from three aspects: extending the reset reference holding time of the analog signal, reducing the collection time of the intermediate charge packet, and extending the collection time of the last charge packet. As a result, the pre-sampling and post-sampling regions of the correlated double sampling are increased by more than 3 times and 1.7 times respectively, improving the sampling reliability. Moreover, the hardware design and performance test verification of the imaging circuit system are completed. The laboratory test results show that the signal-to-noise ratio in all spectral bands of the ultra-large pixel TDICCD is greater than 67 dB, and the stage linearity is better than 99%, meeting the requirements of the camera specifications. Meanwhile, the texture of the on-orbit images is clear, and the spectral bands have distinct layers, further verifying the application of this scheme.