Disclosed are a high-density fiber connector and an assembly method thereof. The connector, adapted for use with a fiber adapter, comprises a connector casing, a ferrule, a spring and a boot, wherein the connector casing has a cross width of 2.5 mm to 4.5 mm. The connector casing comprises a front casing and a rear casing, which lock up one another to form a cavity. The tail of the connector casing is connected with a boot. On the connector casing are sequentially arranged a guide block and an elastic arm from the front toward the back. A fixed end of the elastic arm is oriented toward the tail of the connector, while a free end faces an insert end of the connector and includes a retaining bump. The ferrule 2 is fastened with the ferrule tailstock 3 and penetrates through a through hole at the front of the connector casing. The spring is compressed between the ferrule tailstock and a thrust block formed by inner walls of the connector casing. The provided fiber connector has a significantly reduced cross width of between 2.5 mm and 4.5 mm at the engaging surface without, however, compromising the structural strength and utility functions, such that the fiber connector may be more densely installed.