The invention relates to a highly gassy coal seam group mining gob-side entry retaining Y-shaped ventilation and decompression gas extraction method. The invention is characterized in that: free desorption gas which comes from an adjacent decompression layer and is gathered into a roof plate decompression crack ring and a bottom plate decompression crack ring through crack channels which are formed by mining affection on roof plate coal seam and strata and bottom plate coal seam and strata is extracted in a gob-side entry through an upward extraction gas drill hole which is arranged inside the roof plate decompression crack ring and a downward extraction gas drill hole which is arranged inside the bottom plate decompression crack ring in a roof plate decompression area and a bottom plate decompression area of a gob-side entry retaining gob of a coal face of a primarily extracted coal seam of a highly gassy coal seam group. The highly gassy coal seam group mining gob-side entry retaining Y-shaped ventilation and decompression gas extraction method solves the problem of low extraction rate of the highly gassy low permeability coal seam group, simultaneously solves the ultralimit problem of airflow gas of spatial angles and return airways on the coal face of the primarily extracted coal seam of the highly gassy coal seam group, and realizes extraction utilization of high concentration gas and highly efficient and safe extraction of the highly gassy coal seam group without coal pillars.