The invention provides a method for encoding downhole data by using positive pressure pulses and negative pressure pulses simultaneously. The method for encoding the downhole data by using the positive pressure pulses and the negative pressure pulses simultaneously comprises the following steps that the number of pressure pulse combinations and the number of binary bits are determined according tothe range of data to be transmitted and the required accuracy; conversion of number systems is carried out on a binary system, time is segmented by the converted number systems according to digits, each digit corresponds to a segment, and each segment contains a different number of time slots; and the positive pressure pulses and the negative pressure pulses are generated simultaneously in the time slots contained in each time segment, the number of the positive pressure pulses and negative pressure pulses and positions corresponding to the pulses are arranged, combined and encoded, and an encoding agreement is established to complete the encoding of the downhole data. A downhole data transmission method comprises the steps that encoding is carried out by the method for encoding the downhole data by using the positive pressure pulses and the negative pressure pulses, and then data transmission is carried out. Time frames occupied by transmitting the same amount of data are reduced manyfold, a larger amount of data can be transmitted in the same time period, and the transmission rate is can effectively increased.