The invention provides an optical transmitter with a hybrid modulation format. The optical transmitter is applied to a passive optical access network and a long-distance optical transmission system, wherein the passive optical access network is formed by integrating a wavelength division multiplexer and an optical branching device. The optical transmitter comprises an I/Q modulator 1, an I/Q modulator 2, a delay line interferometer and a Mach-Zehnder modulator. The I/Q modulator 1 is in cascade connection with the delay line interferometer, then is in cascade connection with the I/Q modulator 2 and lastly, is in cascade connection with the Mach-Zehnder modulator. The two I/Q modulators are respectively provided with two data input ports, and the Mach-Zehnder modulator is provided with one data input port. The optical transmitter is controlled to output an optical signal with the self-adaptation hybrid modulation format by controlling the on-off and the signal amplitude of the data input ports and the bit and the phase position delay of the delay line interferometer. By means of the optical transmitter, QPSK modulation, 8 QAM modulation and circular 16 QAM modulation can be achieved, and hybrid transmission formed by various modulation formats in any proportional mode can also be achieved. The optical transmitter can be applied to complex transmission links under the wavelength division multiplexing passive optical network environment, and the frequency spectrum utilization efficiency can be effectively improved.