Screen monitoring methods, screen monitoring devices and screen monitoring system

The invention discloses screen monitoring methods, screen monitoring devices and a screen monitoring system to solve the problem that a bitmap acquired by a client cannot realize equally proportional enlarging or shrinking. The method includes: acquiring screen resolution of a second terminal by a first terminal; sending, by the first terminal, an instruction, of requesting, by a user, for monitoring a preset page through a screen of the second terminal, to a corresponding server of the preset page, wherein the instruction carries the screen resolution of the second terminal; receiving description information, which is returned by the server and for a preset screen monitoring area in the preset page, by the first terminal, wherein the description information is used to enable the first terminal to obtain a bitmap, of which a length-width ratio is the same as the screen resolution of the second terminal, when screen capturing is carried out on the preset screen monitoring area in the preset page which is prese