The invention discloses a pre-splitting blasthole forming and online detonating method for an initial mining tight roof of a fully mechanized coal mining face and belongs to the technical field of suspension treatment of tight roof of coal mining. The method comprises the following steps: S1, forming blastholes in an initial mining open-off cut; S2, forming the blastholes in primary and secondarylanes in advance; s3, forming supplementing blastholes; S4, designing blasthole charging and luting parameters and carrying out online detonation; and S5, carrying out reinforced supporting on the primary and secondary lanes. The method has relatively high field operability and can save the number of drilled holes, lower the cost and shorten the construction period on the premise of guaranteeing apre-splitting effect of the tight roof.