Heralded single photon sources (HSPS) using spontaneous parametric down conversion (SPDC) are widely used in photonic quantum information. However, the excess-photon pair generation in SPDC process is a problem, which results in the events where more than two photons exist in a pulse. Such excess photons degrade the visibility (V) of two-photon Hong-Ou-Mandel interference, and are one of the main error causes in the advanced linear optics photonic circuits. Recently, we have developed a novel HSPS which combines two methods to suppress such excess photon numbers. The first method (A) is to use multiple SPDC sources in one HSPS, where upon the detection of the idler photon from one of the source, the corresponding signal photon is output. The second method (B) is to use cascaded detectors to monitor the photon-pair number generated from the source, where the detector distinguish the single-pair generation from multi-pair generation and thus the excess-photon generation can be suppressed. In this presentation, we report the theoretical calculations how such a source can improve the visibility for a two photon interference. For example, when the average number of pairs from SPDC in a pulse is 0.1, and the detection efficiency is 70%, V= 83.2% for a conventional HSPS. V is improved to 90.3%, 87.1% and 92.7% by using method A, B and our hybrid approach, respectively.