A large-torque chain-guide type constant ratio/continuously variable transmission is disclosed. The transmission comprises transmission rollers (A, B), an endless transmission chain or belt (C) and two chain guiders (D, E) respectively arranged beside the two transmission rollers. Each chain guider comprises n groups of grooved-pulleys, and each group comprises m grooved-pulleys. Each grooved-pulley rotates freely around a grooved-pulley axis, and an angle α is formed between the axis of at least one grooved-pulley in each group of grooved-pulleys and a roller axis of the transmission roller matched with the same grooved-pulley. The angle α enables the chain entering the chain guider and the chain leaving the chain guider to move a certain axial distance, i.e. a chain distance, on the transmission rollers, wherein the chain distance is required to be larger than the width of the chain or the belt. The endless transmission chain passes sequentially through the pulley groove of at least one grooved-pulley in one group and the driving roller under the guidance of the chain guider, and is guided to a driven roller after winding n circles around both the chain guider and the driving roller. Whereafter, the transmission chain passes sequentially through the pulley groove of at least one grooved-pulley in one group and the driven roller under the guidance of the chain guider, and returns to the driving roller to be closed after winding n circles around both the chain guider and the driven roller. The transmission has small size and compact structure, and can output a large torque.