The invention discloses a tension-free continuous cloth feeding device of a single pass digital ink-jet printing machine. The tension-free continuous cloth feeding device comprises a grey cloth frame and grey cloth put on the grey cloth frame and is characterized in that the grey cloth sequentially passes space between a pair of first cloth pressing rollers, a cloth loosening roller, a conveying belt and space between a pair of second cloth pressing rollers to be conveyed to the printing machine, wherein one of the pair of first cloth pressing rollers is connected to a first cloth feeding motor; the cloth loosening roller is arranged below the first cloth pressing rollers; the conveying belt is horizontally put, is arranged below the cloth loosening roller and is connected to a cloth feeding main wheel and a cloth feeding counter wheel, and the cloth feeding main wheel is connected to the conveying motor; one of the pair of second cloth pressing rollers is connected to a second cloth feeding motor; the pair of second cloth pressing rollers are arranged above the conveying belt; the grey cloth coming out of the conveying belt reaches the space between the pair of second cloth pressing roller sequentially through a tension adjusting device and an angular cloth guiding device and then reaches the printing machine through a cloth rectifying device. The tension-free continuous cloth feeding device has the beneficial effects of simple structure, good centering effect and improvement of printing quality.