The invention relates to seal special for a thick oil pump, and belongs to the field of mechanical seal for a pump. The seal comprises a spring seat, a shaft sleeve, a moving ring and a stationary ring; a preloaded spring is embedded among the spring seat, the moving ring and the shaft sleeve; an O-shaped seal ring is arranged between the moving ring and the shaft sleeve; a thrust ring is arranged between the O-shaped seal ring and the preloaded spring; a secondary moving ring is arranged on the shaft sleeve on the other side of the stationary ring; a second O-shaped seal ring is arranged between the secondary moving ring and the shaft sleeve; the other side of the secondary moving ring is provided with a second thrust ring; an annular groove is arranged on the second thrust ring; the secondary moving ring is embedded in the annular groove; the shaft sleeve at the other end of the second thrust ring is provided with a fixed ring; a second preloaded spring assembly is arranged between the second thrust ring and the fixed ring; the fixed ring is fixed on the shaft sleeve; and a secondary sealed chamber is formed between the shaft sleeve and the O-shaped seal ring, the moving ring, the stationary ring, the second moving ring and the second O-shaped seal ring, which are sequentially arranged on the shaft sleeve. By the seal, the sealing effect is improved, and the production cost is reduced.