Low exploration area in deepwater is one of the hot issues in oil and gas exploration nowadays. The development of effective hydrocarbon source rock is a first key question to be answered in early evaluation of source rock of low exploration fields. However, the drilling is scarce and lack of sampling analysis data seriously which restrict the early evaluation of source rock in low exploration area. In response to this challenge, on the basis of borehole data in adjacent areas, through making full use of sequence stratigraphy, organic geochemical and geophysical technology, this article has discussed early prediction of source rock and evaluation method with multiple source rock parameters. And this methodology includes five aspects: (1) analysis of sequence stratigraphy to determine the main interval of source rocks; (2) quantitative prediction method of seismic velocity-lithlogy to determine the thickness of source rocks; (3) prediction of vitrinite reflectance with mudstone absolute velocity to determine the maturity of source rocks; (4) type prediction of organic facies based on the conversion from seismic facis to sedimentary facies and organic facies; (5) comprehensive evaluation to select optimum hydrocarbon generating depression. Then this method is applied to early prediction of the source rocks with marine-continental transitional facies in Huaguang depression. The results indicate that the thickness of source rock in Yacheng Formation shows a decrease from north to south, and source rocks is up to 450m of thickness in the second member of Yacheng Formation. Thermal evolution degree of source rocks is very high overall in Yacheng Formation. Influenced by the burial depth, the maturity degree of source rocks in the third member of Yacheng Formation is the highest. The covered area of hydrocarbon source rock with shallow sea facies is the biggest, but shore swamp facies is the narrowest in the second member of Yacheng Formation. In addition, the distribution area of source rock with shallow sea facies is small, but shore swamp facies is wide in the first and third member of Yacheng Formation, meanwhile, source rocks of fan delta swamp facies are widely distributed. After the comprehensive evaluation, source rocks in the third member of Yacheng Formation is the most favorable and source rocks in the first and third member of Yacheng Formation is less favorable.