A horizontal synchronization signal detection system includes a coarse period estimator and a fine period time estimator. The coarse period estimator estimates a minimum value and corresponding position of each period of a CVBS signal to calculate a coarse period of a horizontal synchronization signal. The fine period time estimator divides the horizontal synchronization signal into a first part and a second part so as to generate a first sum and a second sum by adding signals of the first part and the second part, and detects a middle point of the horizontal synchronization signal when the first sum equals the second sum. The steps of fine-tuning the coarse period to generate a fine-tuned coarse period, extracting the horizontal synchronization signal according to the fine-tuned coarse period, and determining whether the first sum is equal to the second sum are repeatedly executed until the first sum equals the second sum.