A system for preparing xylose liquid by continuously hydrolyzing hemicellulose, comprising a neutralizing unit, an acid-adjusting unit, a feeding unit, a liquefaction ejecting unit, a feed and discharge heat-exchanging unit and a discharge controlling unit, wherein the neutralizing unit comprises a raw material tank, a neutralizing concentrated sulfuric acid pump and a neutralizing pipeline mixer, the acid-adjusting unit comprises an acid-adjusting concentrated sulfuric acid pump, an acid-adjusting pipeline mixer and an acid-adjusting tank, the feeding unit comprises a feed tank, the liquefaction ejecting unit comprises a liquefaction ejector and a liquefaction maintainer, the feed and discharge heat-exchanging unit comprises a plate-type feed and discharge heat exchanger and a first discharge temperature sensor, and the discharge controlling unit comprises a discharge valve and a reflux valve; the raw material tank is used to store hemicellulose alkaline liquid, the neutralizing pipeline mixer is used to perform neutralization reaction for the hemicellulose alkaline liquid and concentrated sulfuric acid from the neutralizing concentrated sulfuric acid pump to obtain a hemicellulose liquid raw material, the acid-adjusting pipeline mixer is used to mix the hemicellulose liquid raw material with concentrated sulfuric acid from the acid-adjusting concentrated sulfuric acid pump to obtain hemicellulose liquid, the acid-adjusting tank collects the mixed hemicellulose liquid the feed tank receives the hemicellulose liquid overflowing from the acid-adjusting tank, the plate-type feed and discharge heat exchanger is used to exchange heat between feed of the acid-adjusted hemicellulose liquid and the xylose liquid obtained by hydrolysis, the liquefaction ejector is used to fully mix the heat-exchanged hemicellulose liquid with external high-pressure vapour and eject the heat-exchanged hemicellulose liquid and the high-pressure vapour together into the liquefaction maintainer, the liquefaction maintainer is used to perform hydrolysis reaction for the hemicellulose liquid and water vapour at a high temperature to obtain the xylose liquid, the first discharge temperature sensor is used to sense a temperature of the xylose liquid obtained by hydrolysis, and the first discharge temperature sensor is interlocked with the discharge valve and the reflux valve to control a flow direction of the xylose liquid obtained by hydrolysis. the neutralizing unit comprises a raw material tank, a neutralizing concentrated sulfuric acid pump and a neutralizing pipeline mixer, the acid-adjusting unit comprises an acid-adjusting concentrated sulfuric acid pump, an acid-adjusting pipeline mixer and an acid-adjusting tank, the feeding unit comprises a feed tank, the liquefaction ejecting unit comprises a liquefaction ejector and a liquefaction maintainer, the feed and discharge heat-exchanging unit comprises a plate-type feed and discharge heat exchanger and a first discharge temperature sensor, and the discharge controlling unit comprises a discharge valve and a reflux valve; the raw material tank is used to store hemicellulose alkaline liquid, the neutralizing pipeline mixer is used to perform neutralization reaction for the hemicellulose alkaline liquid and concentrated sulfuric acid from the neutralizing concentrated sulfuric acid pump to obtain a hemicellulose liquid raw material, the acid-adjusting pipeline mixer is used to mix the hemicellulose liquid raw material with concentrated sulfuric acid from the acid-adjusting concentrated sulfuric acid pump to obtain hemicellulose liquid, the acid-adjusting tank collects the mixed hemicellulose liquid the feed tank receives the hemicellulose liquid overflowing from the acid-adjusting tank, the plate-type feed and discharge heat exchanger is used to exchange heat between feed of the acid-adjusted hemicellulose liquid and the xylose liquid obtained by hydrolysis, the liquefaction ejector is used to fully mix the heat-exchanged hemicellulose liquid with external high-pressure vapour and eject the heat-exchanged hemicellulose liquid and the high-pressure vapour together into the liquefaction maintainer, the liquefaction maintainer is used to perform hydrolysis reaction for the hemicellulose liquid and water vapour at a high temperature to obtain the xylose liquid, the first discharge temperature sensor is used to sense a temperature of the xylose liquid obtained by hydrolysis, and the first discharge temperature sensor is interlocked with the discharge valve and the reflux valve to control a flow direction of the xylose liquid obtained by hydrolysis.