The invention discloses a 9-gear twin-countershaft helical gear lock pin synchronizer transmission. Double countershafts and a large center distance are adopted by a main transmission part; all first, second, third and fourth speed gears, a climbing gear and a reverse gear take the shape of a helical gear; the front and rear ends of a main shaft are provided with a main shaft front positioning mechanism and a main shaft rear positioning mechanism respectively; a double cone lock pin synchronizer is arranged between the first and second speed gears; a single cone lock ring synchronizer is arranged between the third and fourth speed gears; the reverse gear and the climbing gear are connected with a sliding gear sleeve; a secondary transmission part is provided with a planetary gear train and a widened double cone lock ring synchronizer; and the main shaft is connected with a sun gear in the secondary transmission part through a spline transition sleeve. According to the 9-gear twin countershaft helical gear lock pin synchronizer transmission, full synchronizer gear shift is realized from the first to fourth speed gears, and meanwhile, the widths of the reverse gear, the climbing gear and the first gear are correspondingly increased, so that the service life at a low-gear zone during heavy load is prolonged, the gear shift performance of a high-gear zone is improved, and the working reliability of the transmission is also improved; and the 9-gear twin countershaft helical gear lock pin synchronizer transmission has the advantages of labor saving in operation, stable gear shift transmission, low noise and long service life.