A PN-junction varactor in a BiCMOS process is disclosed which comprises an N-type region, a P-type region and N-type pseudo buried layers. Both of the N-type and P-type regions are formed in an active area and contact with each other, forming a PN-junction; the P-type region is situated on top of the N-type region. The N-type pseudo buried layers are formed at bottom of shallow trench field oxide regions on both sides of the active area and contact with the N-type region; deep hole contacts are formed on top of the N-type pseudo buried layers in the shallow trench field oxide regions to pick up the N-type region. A manufacturing method of PN-junction varactor in a BiCMOS process is also disclosed.